A browser tab (or simply a tab) is a web organizer for Internet browsers first featured in NetCaptor (SimulBrowse) by Adam Stiles, In 1997. It allows you to open and organize multiple web pages at once without opening a new browser.
A taskbar is the piece of slab that runs across your screen (usually located in the bottom part of your screen) which holds the running applications and shortcuts. The taskbar is a Windows specific software. Though Linux also has a similar function like this, the term Taskbar is commonly associated with Windows machines.
A web browser is a piece of software or program that runs on your computer which enables you to browse or connect to the Web (commonly referred to as the Internet). Web browsers interpret web pages being sent (or served) by web servers and allows you to interact with it depending on how the web pages were made.