Many contracts of employment contain express terms specifying permitted absences.
Examples could include:
In some cases, e.g. for holidays, antenatal appointments, sickness absence and temporary lay-off, there is a statutory entitlement to pay. In other cases, it will depend on what it says in the contract. Details will be in your contract, or in the written statement of particulars which sets out your terms and conditions of employment. Your employer must provide you with this written statement within 8 weeks of starting work.