If an account has a fixed term, this is the length of time for which you'll need to lock your money away to get the advertised rate. Some providers will allow you to withdraw some or all of your money before this term ends, but you'll usually be penalised with fees or a loss of interest.
An ISA is a type of account which allows you to save without paying tax on the interest you earn. There are several different types of ISA- the most common is a cash ISA, in which every adult over the age of 18 can save up to £5,760 each year. There are also investment ISAs- commonly known as stocks and shares ISAs- where you can save another £5,760 on top of your cash ISA allowance, or any amount up to the full total of £11,520 if you decide not to use your full cash ISA allowance. Finally, there are Junior ISAs which can be opened for children under the age of 18.
A one off amount of money an individual wants to pay into an account. Most accounts with a fixed term will require you to pay in a lump sum and will not allow you to make any more deposits, whereas instant access accounts may allow you to make regular payments into the account.
The amount allowed to be invested in an ISA account which is free of income tax. This is currently £5,760 in a cash ISA or £11,520 in an investment ISA.