Some of these terms are 'express' terms – that is they are expressly or specifically stated, either orally (at the initial interview, say) or in writing. Express terms include things like pay, hours and holidays.
The law states that certain express terms must be put in writing and handed to the employee in the form of a written statement of particulars within one month of starting work.
There are other contractual terms called 'implied' terms. These are not expressly or explicitly stated because, in the main, they are fairly obvious to both parties to the contract of employment.
Occasionally, the courts will imply a term in a contract of employment where an important term has been left out.
An important implied term is the duty of mutual trust and confidence, which is implied in every employment contract.