Rapid growth of WWW poses unpredictable challenges for the crawlers and search engines. Focused Crawler main aim is to selectively seek out pages that are relevant to pre-define set of topic rather than to exploit all regions of web. In this paper a review of focused crawler approaches have been presented which is classify in to five categories: Priority base crawler, Structured base crawler, Leaning base crawler, Context base crawler and Other focused crawler. There is also secrecy involved to protect against search spamming and ranking functions, thereby it is rare to announce or publish complete web crawling architectures. In this work, we propose focused web crawler architecture to expose the underneath secrets of web crawling implementation.