To be able to use an IR led effectively it needs to be modulated.
That is it needs to be turned on and off at a certain frequency.
Do not confuse this with the frequency of IR this is the frequency of turning
the LED on and off just like you would do with a normal light LED.
The reason for this is that the receiver can then have a filter that
would not accept except the frequency of the Emmitter so that it will
be able to avoid normal IR that comes from lamps and sunlight etc.
So with this setup the Receiver and Emmitter would have a correspondance
that would make the receiver sure that when it receives the on and off
the emmitter is giving it will respond with assurance that it is a real signal.
It is said, that to the one who's only got a hammer, every problem looks like a nail.
IR is used in so many apps and while some of them (mainly remote control and the like) use a carrier wave, other apps would only be worsened by the carrier.
Not every app use an integrated demodulating remote control receiver !
But strictly speeking an IR LED is also an emmitter, but I think this is difference
that some people may use to distinguis between an unmodulated IR LED and
a modulated one.
Not only strictly speaking, but speaking in every which way (but nonsense), LED means Light Emitting
Diode as I wrote. This is not a case of "some people" inventing their own terms, but simply that the term emitter is sometimes used alone to distinguish it from a receiver, when the subject is allready known to be about LEDs and photo diodes.
Modulated vs. unmodulated (i.e. carrier wave or not) has nothing to do with it being an emitter.
Now I'm running out of ways to drive the point through, so please read it twice, if it still gives you any doubts, or look up the word "emit" in a thesaurus.