What is Design Exchange Format (DEF)?

A specification for representing logical connectivity and physical layout of and integrated circuit in ASCII format

Example:  

A DEF file is used to describe all the physical aspects of a design, including 

- Die size

- Connectivity 

- Physical location of cells and macros on the chip. 

It contains floor-planning information such as 

- Standard cell rows, groups

- Placement and routing blockages

- Placement constraints

- Power domain boundaries. 

It also contains the physical representation for pins, signal routing, and power routing, including rings and stripes.