A limit order is a type of order where you can set up a trigger to automatically buy or sell an investment when it reaches a price you’ve specified, or better!
For example, you would place a buy limit at a price lower than the current market value so that if the stock price fell, your limit order would kick in and attempt to buy the shares you wanted at a price you're happy to pay for them.
On the flip side, you would place a sell limit at a higher price than the current market value so that once the stock price increased enough to provide you with whatever you consider a decent return on your investment, your limit order would kick in and attempt to sell your investment for you.
Important:
When entering a cash amount for a buy limit, this will also cover stamp duty. You may find that the amount of shares that you receive is lower than expected.
For example; if you select a limit price of £5, and reserve £10 cash in order to receive 2 shares, you may actually only receive 1 share due to stamp duty being deducted.