If you seldom see your grandmother because she lives far away, you might be grateful for the opportunity to visit her over the summer. Use the adjective seldom to refer to things that don't happen very often.
A near synonym is rarely. Seldom is a Middle English word, from Old English seldum, a spelling alteration of seldan "strange, rare." In Old English, the spelling seldum came about by analogy with forms such as Old English hwilum "formerly, at one time," from hwil "time, while."