Visual Basic is a modern, object-oriented programming language designed to simplify development for Windows. Visual Basic was moved to the .NET platform in 2001 and renamed Visual Basic .NET, which broke earlier programs written in VB6 and before. The language itself, however, has not changed much.
As its name suggests, Visual Basic is historically related with BASIC, but today it is only noticable in the syntax.
Mono is a project which attempts to provide a CLR for non-windows systems, and with it support for Visual Basic outside of Windows.