If something is infrequent, it does not happen often.
例句
...John's infrequent visits to London.約翰僅有的幾次倫敦之行
英英詞典釋義
Adverb
1. not many times;
"in your 1850 church you not infrequently find a dramatic contrast between the sumptuous appointments of the building itself and the inhuman barrack-like living conditions in the church room"