A limit order is an order to buy at no more than a specific price or to sell at no less than a specific price.
The purpose of a limit order is to give the user control over the price at which the trade is executed. However, this does not mean the order will be filled, as this is dependent on other traders being willing to buy or sell at this price.
For situations where the certainty of execution is a priority over the price of execution, please see 'what is a market order?'.
Buy limit orders are only able to be executed at the limit price, or lower. For example, if a user doesn't want to pay more than $1400 for 1KVT, his order would not be filled at $1401. However, if someone has put a sell limit order in for $1399, their order would be filled.