Surface body is a general term that describes connected zero-thickness geometries such as single surfaces, knit surfaces, trimmed and filleted surfaces, and so on. You can have multiple surface bodies in a single part.
You can select a surface body from the graphics area using Filter Surface Bodies 
on the Selection Filter toolbar. You can select all types of surfaces with Filter Surface Bodies.
The pointer changes to
when it is over a surface body. Surface bodies can include:
- Single face surfaces
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Multiple face surfaces
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Knit surfaces
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Filleted surfaces
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Trimmed and extended surfaces
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Imported surfaces
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Planar surfaces and mid surfaces
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Surfaces made by extrude, revolve, loft, sweep, offset, radiate, or fill
To select a single face in a complex surface body, use
Filter Faces 
on the Selection Filter toolbar.