All xxD, xxxD, and xxxxD bodies have ~16x24mm sensors.
EF-S lenses work on all xxxxD, xxxD, and xxD bodies. EF lenses work on every single EOS camera ever made.*
EOS xxxx is for the lowest-end bodies, mostly meant for beginners or the "soccer parent" crowd. There are tons of film bodies in this class, and the XS (the 1000D) is the first of the digitals.
EOS xxx is for bodies with the size, weight, and control layouts of the xxxx series, but most of the features and performance of the xx series. The Rebel Ti (film) and the Rebel XTi (digital) fit into this category.
EOS xx is for heavyweight advanced amateur bodies, such as the film Elan series and the digital 40D.
EOS x (except for the 1's) vary wildly in features, but all are meant for high-end "semi-pro" use of some kind. The 5D is a xxD class camera with a ~24x36mm sensor; the 3 is a rugged and fast film body; the 5 is "poor man's 3"; almost as fast, almost as rugged, but good enough for many professional situations.
EOS 1 cameras are the professional bodies; extremely rugged, fast and reliable. They're the kind of cameras you take into warzones or hurricanes. If it has "Ds" at the end it means it has a ~24x36mm full-frame digital sensor (the "s" stands for studio); "D" on its' own means a ~28x19mm sensor. Anything else is a film camera (1, 1N, 1V).
( *The old manual-focus-only EF-M film body is the sole body exception, but you'll never run into it in real life. )
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The naming scheme is actually not too complex.
A "D" at the end means digital.
All xxD, xxxD, and xxxxD bodies have ~16x24mm sensors.
EF-S lenses work on all xxxxD, xxxD, and xxD bodies. EF lenses work on every single EOS camera ever made.*
EOS xxxx is for the lowest-end bodies, mostly meant for beginners or the "soccer parent" crowd. There are tons of film bodies in this class, and the XS (the 1000D) is the first of the digitals.
EOS xxx is for bodies with the size, weight, and control layouts of the xxxx series, but most of the features and performance of the xx series. The Rebel Ti (film) and the Rebel XTi (digital) fit into this category.
EOS xx is for heavyweight advanced amateur bodies, such as the film Elan series and the digital 40D.
EOS x (except for the 1's) vary wildly in features, but all are meant for high-end "semi-pro" use of some kind. The 5D is a xxD class camera with a ~24x36mm sensor; the 3 is a rugged and fast film body; the 5 is "poor man's 3"; almost as fast, almost as rugged, but good enough for many professional situations.
EOS 1 cameras are the professional bodies; extremely rugged, fast and reliable. They're the kind of cameras you take into warzones or hurricanes. If it has "Ds" at the end it means it has a ~24x36mm full-frame digital sensor (the "s" stands for studio); "D" on its' own means a ~28x19mm sensor. Anything else is a film camera (1, 1N, 1V).
( *The old manual-focus-only EF-M film body is the sole body exception, but you'll never run into it in real life. )