Relative address means an address specified by indicating its distance from another address, called the base address. For example, a relative address might be B+15, B being the base address and 15 the distance (called the offset).
Types of Addressing
Relative and absolute addressing are used in a variety of circumstances. In programming, you can use either mode to identify locations in main memory or on mass storage devices. Relative addressing is always in bytes and usually, you do not need to worry about addresses unless you are a programmer.
Relative Addressing (References) in Spreadsheets
In spreadsheet applications, you can use either mode to designate a particular cell. Programs, like Microsoft Excel uses relative addressing by default. This means you can copy a formula and it increments the letters in the formula as a default option. Absolute Addressing happens when you lock a formula to the cell so it does not change when pasted to another cell. In Excel, relative and absolute addressing is more frequently called relative and absolute references.
Image: This Excel Help screen describes changing relative and absolute references.