Co-branding refers to the process when two brands come together for an alliance and brand a product together to utilize the synergies between the two brands.
For example: A shoppers Stop membership card co- branded with HDFC
There can be 2 types of co-branding:
Ingredient co-branding: An existing product of one of the brands is used and co-branded with the other
Composite co-branding: A new product/service is created by both the brands together which would not have been possible by the two brands alone.