A microsite (sometimes known as a minisite) most commonly refers to a secondary website which is the subsidiary relation to its parent website. Generally this site will be regarded as a separate creation, due to its diversity in content or even a different URL. A microsite, also referred to as a weblet generally has its own domain name, this is know as niche marketing.

See also:
Niche Marketing
Cost per acquisition (CPA)
Cost per click (CPC)
Reciprocal links
Ad rotation
Ad impression
RSS
E-Marketing
User Session