Additional free shares issued to existing shareholders in a fixed ratio, funded from the company's reserves.
A bonus issue gives existing shareholders extra shares — for example, a 1:1 bonus means you get one additional free share for every share you already hold — funded out of the company's accumulated reserves rather than fresh capital. The total value of your holding doesn't change immediately (the share price adjusts down proportionally), but bonus issues improve liquidity by increasing the number of shares in circulation and are often read as a signal of management confidence.