Definition of Casual

Casual:

A relationship with a girl where you are pseudo-boyfriend and girlfriend, but mainly just have sex.
Source: Urban Dictionary

Casual:

You met with on occasions and known only superficially (eg. a casual friend)

Casual Dating:

Casual Dating is a loose way of dating.
Being able to say Boyfriend Girlfriend yet be able to have sex with as many people as you want.

Tammy - "I want to get back together"
Chris - "I think we should just try
Casual Dating." Tammy - "YOU PIG!!!"

Source: Urban Dictionary

Hey, isn't this the same as being in an "open relationship"?

See "Open Relationship" Blog below.
Click here for Yaletown Girl's definition of Open Relationship.

Casual Sex:

Sex without serious intent or commitment