An unsymmetrical alkene is an alkene in whose molecule the pair of ligands on one doubly bonded carbon is different from that on the other.

eg. 1:

In 1, one doubly bonded carbon bears two methyl groups and the other a methyl group and a hydrogen atom.  Thus, 1 is an unsymmetrical alkene.

eg. 2:

In 2, one doubly bonded carbon bears two methyl groups and the other a methyl group and an ethyl group.  Thus, 2 is an unsymmetrical alkene.

eg. 3:

In 3, one doubly bonded carbon bears a methyl group and a hydrogen atom and the other an ethyl group and a propyl group.  Thus, 3 is an unsymmetrical alkene.

In an organic molecule, a carbon-carbon double bond in which the carbon atoms bear different pairs of ligands is called an unsymmetrical double bond.

eg:

see also symmetrical alkene