Business Process Execution Language is the latest standard in Web Services. Previously IBM and Microsoft had their proprietry technologies, WSFL ( Web Service Flow Language ) from IBM and XLANG by Microsoft. BPEL is a standard obtained by coalescing the two technologies. The Web services designed by using BPEL are used for B2B transactions which can last for a longer period of time.
WSFL i s based on the concept of directed graphs whereas XLANG is based on block structures language. BPEL combines both and creates a rich set of vocabulary. A BPEL process is an XML document generated with graphical design tools by business analysts rather than programmers.
Basically Web Service is a web method sitting on the WWW and executing business processes. Various WEb Services can be combined to create a complex business process. They can act as building blocks and create inter or intra Enterprise applications.