Both are Individual Savings Accounts. Both shelter your returns from tax. The annual allowance is £20,000 and you can split it across ISA types in any combination you like. The difference is what sits inside the wrapper.
Outside an ISA, interest on savings is taxable above your Personal Savings Allowance (£500 for higher rate taxpayers, £1,000 for basic rate). Capital gains on investments above the annual exempt amount are taxable too. Inside an ISA, you pay no tax on interest, dividends or capital gains.
Functions like a savings account, but interest is tax-free regardless of amount. The rate you earn is fixed or variable depending on the product. In higher interest rate environments, Cash ISAs become more competitive. Best suited to money you'll need within one to five years, an emergency fund top-up, or savings where you can't afford any risk to the principal.
Holds investments: funds, shares, bonds. Returns aren't guaranteed. The value goes up and down. Over 20 years or more, diversified investment portfolios have outperformed cash savings in almost every historical period. The gap compounds significantly over long timeframes. Best suited to money you won't need for at least five years, ideally ten or more.
If the timeline is short or the money is for something specific, Cash ISA. If the timeline is long and you can tolerate fluctuation, Stocks and Shares ISA. Many people use both for different purposes.
Keeping long-term money in cash and watching inflation erode its real value over a decade. If you have money you genuinely won't need for ten years, cash savings are unlikely to be the right home for it.