Tom got a letter from him just a little while ago.
They moved to a new housesome time ago (=a fairly long time ago).
We had our bicentenary celebrations not that long ago.
WORD CHOICE: WORD CHOICE: ago, before, previously Use agoto say how much time has passed from the time something happened to now, the time of speaking• I saw her a few minutes ago.• We went to Madrid two years ago.Use beforeto say how much time passed from the time something happened to a time in the past• We went to the same hotel where we stayed two years before.Previouslyis used in the same way, but is more formal• The meeting was a follow-up to one that had been held four days previously.GRAMMAR!! Do not use a preposition ('at', 'in', 'on' etc) before a phrase with ago• They first met fifteen years ago (NOT at/in fifteen years ago).!! Do not use 'since' or 'before' with ago• I came to the USA two months ago (NOT since/before two months ago).!! Use the past tense, not the present perfect, with ago• I started (NOT I've started) a new job a few weeks ago.
Definition from the Longman Dictionary of Contemporary English Advanced Learner's Dictionary.