What do γ (gamma) and λ (lambda) mean in organic chemistry?

From the Wikipedia entry on Cyhalothrin:

Pyrethroids such as cyhalothrin are often preferred as an active ingredient in agricultural insecticides because they are more cost-effective and longer acting than natural pyrethrins. λ-and γ-cyhalothrin are now used to control insects and spider mites in crops including cotton, cereals, potatoes and vegetables.[5]

Lambda-cyhalothrin
Cyhalothrin gamma.svg
λ-cyhalothrin (racemic)

Compounds
Lambda: λ-Cyhalothrin
(RS)-α-cyano (1RS,3RS): Cyhalothrin
Gamma: γ-Cyhalothrin

Gamma-cyhalothrin[6] and lambda-cyhalothrin1 are the active ingredients in the current commercial products based on cyhalothrin. Both are cyanohydrin esters of cis-3-[(Z)-2-chloro-3,3,3-trifluoropropenyl]-2,2-dimethylcyclopropanecarboxylic acid. All of the insecticidal activity is due to the proportion of absolute stereochemistry (1R) in the mixture.[7] The active isomer of deltamethrin, (1R)-cis-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropanecarboxylic acid, has the same stereochemistry.

Cyhalothrin and deltamethrin acids.
γ-cyhalothrin (a single chiral isomer) is indeed twice as active as λ-cyhalothrin on a weight-for-weight basis. The latter is racemic and contains the (1R) and inactive (1S) isomers in equal amounts.

I have tried and tried on my own to find out what lowercase gamma and lowercase delta could mean here, but I can’t find an answer…

Also what does, AND Enantiomer mean? Or, A.N.D. Enantiomer?