To come together to form one mass or whole. The separate streams coalesced into a single river.
To unite or merge into a single body or group. The various factions coalesced to form a powerful political party.
To cause (separate elements) to unite or merge into a single whole; to fuse. The editor managed to coalesce the various reports into one comprehensive document.
Computing: to return the first non-null or first available value from a list of expressions. The query used COALESCE(user_name, 'Guest') to supply a default when the column was empty.