Symbols
A symbol is a power or ground object, an off-page connector, a hierarchical port, or a title block. You can place power and ground symbols, and you can edit their names before or after placing them.
You can also edit the text associated with the symbols. The name of a power symbol becomes the name of the global net that is created.
Placing ground symbols
The main feature of symbols is that it is not necessary to allocate a PCB footprints to them because they do not represent physical, but lebels, flags, virtual interconnection item (as net aliases) or non-electrical objects (title blocks).