ILC is Interchangeable Lens Camera, basically meaning that you are able to shift between different lenses. The opposite to an ILC is a camera that comes with the lens fixed – as you know it from your smartphone or a point and shoot camera like the Sony RX100.
Although ILC judging from the name should cover all types of cameras with interchangeable lenses, the term ILC for reasons beyond me often is used to describe mirrorless cameras with interchangeable lenses. If the camera has a mirror built into it, the term DSLR is more frequently used.
To mitigate this confusion, some use the term MILC instead of ILC to underline that it is a Mirrorless Interchangeable Lens Camera they are talking about.
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I agree with you. The key feature of an interchangeable lens camera is its ability to detach and swap lenses. This includes film cameras and digital cameras.