Pragamatically speaking, entry-level means the cheapest camera any manufacturer currently offers. It can also mean the category of all such cameras — and as such, it would be theoretically possible for a company to make all or no entry-level cameras, even if they had different options. I don't know of anyone who has decided to leave the higher models off the table, but some of the niche brands like Sigma or Leica arguably have no entry level models, while one could say that both of Nikon's D3xxx and D5xxx series are entry-level. On the other hand, the Hasselblad H5D-40 is the company's "entry-level" medium format DSLR -- at $13,000.
So, overall, there is no fixed list of features, or even price category. The common factor is that entry-level models are cameras marketed at uncertain first purchasers, either first in a certain category (like first DSLR, or first medium format, or first interchangeable-lens camera), or first camera entirely. As such, the key points tend to be:
Priced as low as can be gotten away with
This in turn has two aspects: first, features are eliminated to cut costs. Second, cameras are often priced aggressively with lower margins in order to get people in the door.
Instant ease-of-use a design priority
A camera with many buttons and dials is much easier and faster to use once you've mastered the fundamentals of photography and once you know what and where the controls are on that particular camera. But this can have a steep learning curve, scaring away new users. So, entry-level cameras often have simplified user interfaces, with a high focus on automation.
Because this is a marketing construct, I'd argue that if you are really planning to enter photography, "entry-level" is not really for you. Aand, in fact I do argue this in another question on this site -- see Are there disadvantages to a prosumer camera for a beginner, aside from cost?.
Feature selection relative to market position
Cost-cutting isn't the only reason for feature selection, though. Some features are very low cost but withheld from "entry-level" models simply to avoid competing with the same brand's higher models. For Canon and Nikon, their own lines are bigger competition than Pentax, Sony, Olympus, Sigma, or etc., which means that in general, the big two tend to intentionally withhold features from the entry-level models, whereas the smaller companies actually push higher-end features "down the stack" in hopes of drawing attention and discerning buyers.
Also because this is a marketing construct, it it's often the case that such cameras basically do come with a sticker which says "entry level", although it will be couched in other phrases. For example, here are the headlines on the product pages of the three main manufacturers still invested in DSLRs:
- Nikon D3200: "Simply Effortless. Simply Stunning"
- Canon EOS Rebel T3: "The Beauty of Simplicity"
- Pentax K-500: "Beyond Basics" (but note that the first line of copy after that is "Jump right into digital photography with a comfortable, approachable DSLR, paired with high quality specifications that go above and beyond entry level...")
The theme here is Entry-level cameras are marketed as able to produce beautiful, stunning images with little effort. Everything else, from the features available to the construction to the price point is really in service of that message. The fundamental goal is to hook you into photography and into that specific brand, so you buy accessories, lenses, and eventually, hopefully, a more expensive body with higher profit margins.
As a rough generalization in the current market, entry level DSLR models:
- are made less tough (cheaper materials, lower shutter count rating, no weather sealing)
- come with a low-cost, versatile zoom lens (usually 18-55mm), because buying lenses is intimidating and the targeted buyer won't have any to begin with
- pentamirror instead of more expensive pentaprism, and generally a lower-cost viewfinder
- have less sophisticated autofocus — slower, fewer points to select from
- have no top LCD or dual control wheels — not just added expense, but they look hard
- emphasize "scene modes" and other hand-holding features, and other more advanced software-based features like auto-bracketing may be missing
The overall category of entry-level DSLRs usually have APS-C or smaller sensors,
but, as in this review, one can consider cameras like the Canon EOS 6D or the Nikon D610 entry level within their category. Additionally, not all cameras with smaller-than-35mm-film sensors are entry level, with some nice "mid-tier", "intermediate", or "prosumer" APS-C models in the $1000-$2000 price range. Or, consider Nikon's 1 line, which features a smaller-than-APS C sensor. There, the "S" models like the Nikon 1 S2 are designed to be "entry level" and the "V" models like the Nikon 1 V3 are the "flagship" models — all with the same sensor size.
Another particular quirk of DSLR Nikon's lineup is that the lower models do not contain a motor to drive autofocus on lenses without a built-in motor. There's a general trend towards lens-based AF motors (and in fact, all Canon cameras have no motor in the body), so this may or may not be an issue, but if you want wide lens compatibility it's worth considering -- to Nikon, this was something reasonably left out of the entry-level.
Pentax's current "entry-level" model, the K-500, demonstrates the "smaller maker" effect here, as that model has dual control dials and a 100%-view pentaprism finder. In fact, on that page, the marketing copy includes the phrase "beyond entry level" -- but this clearly is an "entry level" model. (This isn't meant to be a pitch for Pentax, although I do use a higher-model Pentax myself; there are other balancing considerations which clearly make the entry-level models from other makers appealing, although as I previously noted I think that anyone serious about getting into photography should look at a higher segment anyway.)