Definition according to the oxford english dictionary:
In information security, integrity is the principle that requires information to maintain its precision.
The way we might maintain data integrity may include one or more of the following
A checksum is a number outputted by a mathematical function to verify that a data block has not been changed, examples like CRC’s, hashes etc, each type of checksum has pro’s and con’s either in time to create or potential for a changed data block to output the same checksum as the unmodified block. Whilst a checksum provides some assurance that the data block has integrity is does not ensure authenticity.
Only the correct people can amend or delete data. Often you will see the acronym ACL (Access Control List) this is the implementation of access control, each ACL holds a list of Access Control Entries (ACE), i.e. allowed, denied audited for a particular data item for a person or system. This is deep subject in itself which we will dive into later.