Limit buy and limit sell orders are the two sides of the limit order, which is covered in full under that entry, including how such orders sit in the book and how they compare with other order types. This page explains the two names as they appear on trading screens.
A limit buy tells an exchange or broker to purchase an asset only at a chosen price or lower. A trader who sees bitcoin at 60,000 but wants to pay no more than 58,000 places a limit buy at 58,000; the order waits in the order book until a seller accepts that price or the trader cancels it. A limit sell is the mirror image: an instruction to sell only at a chosen price or higher, often used to take profit at a target level.
The names exist because crypto and retail trading apps usually show separate "buy" and "sell" buttons, each with a "limit" option, so users meet the terms in that form. A limit buy placed below the current ask price, or a limit sell above the current bid price, usually adds liquidity and may earn lower maker fees. The trade-off is certainty: the price is protected, but the order may never fill. By contrast, a market buy or market sell fills at once at whatever price is available.