An open cheque is one

A cheque is an instruction to a bank to pay a stated sum of money. Cheques are classified as open or crossed based on how they can be paid. An open cheque has no crossing lines drawn across its face, which means the person holding it can walk into the bank and collect the money over the counter in cash. A crossed cheque, by contrast, has two parallel lines drawn across it and must be paid into a bank account rather than cashed directly, which makes it safer if the cheque is lost or stolen.

The other descriptions do not define an open cheque. A cheque with no name written on the payee line is a bearer cheque, not necessarily an open one. A cheque with no amount filled in is simply an incomplete or blank cheque, which is not valid for payment. Writing the amount only in figures (without also writing it in words) is a drafting error that a bank may reject, not a classification of cheque type.

Examination reminder: remember the direct link between 'open' and 'cashed over the counter' - it is the opposite safety feature of a crossed cheque.