If a domain is already registered and is in use with an active website there is little chance that the current registrant will release it. If however the domain is dormant and shows nothing or just a parking page (page of links) it may be obtainable.
If the domain is not being cared for there is a good chance that it will not be renewed and in that case it will be deleted around 90 days after it expires. This is referred to as the domain dropping. There are many companies similar to eetc who catch dropping domains and this is a fiercly compettitive market. Domains that drop are typically registered in less than a second (well the good ones are).
If the domain shows a parking page ther is a good chance that the domain is held by a domain warehouse, like eetc, so the domain is probably for sale.
