Convenience sampling means sampling according to who/what is available; stratified means you sample sub-populations separately (e.g. sample from registered Republicans and Democrats to find a poll average for a congressional race) and a census is an attempt to sample a whole population.
Mar 18th, 2015
(and I think in that other question you posted the person answering may be incorrect - I would think that picking names from a hat containing only seniors would be stratified sampling, i.e. sampling from a subpopulation - in that case, the subpopulation is seniors).