It seems there are almost as many different types of polls as there are advocacy groups. We have polls of Republicans, Democrats, Independents, Libertarians, Greenies, Catholics, Evangelicals, dog lovers, etc., etc..
We have polls of everyone, of those over 18 (often referred to as adults), of registered voters, likely voters, and most likely voters.
We also have advocacy polls in which corrupt pollsters focus on a database known to provide the answers they are seeking. The Chicago Tribune was accused of doing just that during the George Ryan/Glenn Poshard campaign for Illinois governor in which they “showed” a pending blowout in favor of George Ryan. In reality, Ryan beat Poshard by less than one point but the Tribune got what they wanted: a moratorium on the death penalty immediately after Ryan was sworn into office .