File extensions used in SharePoint/What is breadcrumb in Share Point

 infopath file extension  - .xsn
 List or Library template - .stp
 site template extension - .wsp
 Asp.net Server object model - .wsp
 Silverlight Client object model -.xap

What is breadcrumb in sharepoint?

• Breadcrumb is a navigation which was shown on the top of the SharePoint site.
• SharePoint 2010 uses breadcrumb navigation to let users keep track of where they are.
  
  Breadcrumbs in SharePoint look like this by default:

  Team Site > Project Site > Shared Documents

  See the following image