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.
Similar meaning, but 近頃 is more formal and often used in writing.
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.