Geometric Isomers are compounds with different spatial arrangements of groups attached to the carbons of a double bond. In alkenes, the carbon-carbon double bond is rigidly fixed. Even though the attachment of atoms is the same, the geometry (the way the atoms "see" each other) is different.
When looking for geometric isomers, a guiding principle is that there MUST BE TWO DIFFERENT "GROUPS" ON EACH CARBON OF THE DOUBLE BOND. A "group" can be hydrogen, alkyls, halogens, etc.