OK, so hands up who knows the difference? Hmm, just as I thought, not many. Don’t worry about it, nor did I until just now!
Rather than rambling on (as usual), I’ll just point you at a StackOverflow question where this was answered as clearly as this is likely to be answered anywhere!
By the way, if you just query your EF context and don’t explicitly convert your results, you’ll end up with an IQueryable<T>. If you use .AsEnumerable(), you’ll end up with an IEnumerable<T> (surprisingly enough).