Deposit
A deposit is a part payment a client makes before you start a project, agreed in the proposal, which confirms they're committed and pays for the time you set aside.
What it means
A deposit is the first part of the price, paid up front. It does three jobs: it shows the client has really decided, it pays for the week you've kept free for them, and it gives you both a clear start date. The rest is paid later, usually at launch or in agreed stages.
Asking for one is normal. Done well, with the amount and the timing written into the proposal, it makes you look organised, not suspicious.
An example
A dog groomer says yes on a Friday call. Your proposal says the project starts when the deposit arrives, so you send the deposit invoice that afternoon. It's paid on Monday and you start on Tuesday. If her business partner had wanted to wait until spring, you'd have found out before doing four days of work, not after.
One rule worth keeping
Start when the deposit has arrived in your account, not when the client says it's been sent. Bank transfers can take a few days, and a message saying "paid" isn't the same as the money being there.
In Volant
Clients pay through your own Stripe account, and a payment counts as received only when Stripe confirms it, so a message saying it's paid doesn't start the work.