Refers to the recent period of time, similar to このごろ or 近頃. Often used in casual conversation.
These days I'm so busy I can hardly take a break.
Lately he doesn't go out much.
Compound of 年頃 (としごろ, 'around this time of year') and 日頃 (ひごろ, 'these days'). The exact historical derivation is uncertain.