1. A particularly fortuitous, beneficial, or productive year. It's been a big year for our company: we've grown from a minor start-up to a real contender in the market.

2. A birding competition or undertaking in which one attempts to identify as many unique species of birds as possible within a calendar year, often within a specific geographical area. We might not win any cash or prizes, but the local big year offers a unique chance to improve my birding techniques.