A somewhat formal or hobbyist term for stamp collecting; in casual conversation, 切手収集 (きってしゅうしゅう) is more common.
His hobby is philately; he collects stamps from all over the world.
郵趣の雑誌を定期購読している。
I subscribe to a philately magazine.
philatelist; stamp collector
Compound of 郵 (ゆう, 'mail') and 趣 (しゅ, 'taste' or 'interest'), literally 'mail interest'. The exact origin is uncertain, but it was likely coined in the early 20th century as a translation of 'philately'.