in PBP, CON is used to define a software constant, in asm it should looks like

YourConstantVariable = .25

or
#DEFINE YourConstantVariable .25

Using pre-defined constant here and there, allow to have a better readable code, and also allow to do some changes without having to scroll the whole code.

For a 12F675 asm example.. well, first google hit gave me
http://www.jbgizmo.com/page29.htm