I remember learning a specific name for words whose meaning depends on the time or location of their use, but as this was when I was in middle school (about 10 years ago), I can't remember what exactly that name is.
My teacher gave the example of here, which means "Chicago" when spoken by a person in Chicago, "Egypt" when spoken by a person in Egypt, etc. There are also time equivalents, such as now (the meaning of which is constantly changing), soon, today, yesterday, and tomorrow. As I'm writing this, today refers to April 14, 2015; yesterday refers to April 13, 2015; and tomorrow refers to April 15, 2015. However, on any other date, those words would mean different things.
I thought that these might be called relative words since their meaning is relative to the circumstances of their use, but when I searched for that phrase, it seems to have a much broader meaning, referring to any "word that does not have an exact definition." This could be words like big, small, short, tall, dumb, smart, etc.—You are tall compared to a mouse, but you are not tall compared to an elephant.
I remember that the word I learned was specific to words whose meaning altered according to place and time, so I'm looking for something more specific than relative word.