The current grid
The concept of current grig is mainly linked to the DocumentsPage, that shows different grids at the same time (each grid has a specific content but they're all related).
Documents Page
MechworksPDM in its Documents Page always activates a grid as current so that every such action will apply only to it.
The current grid is the one with the columns header highlight:
Tree Page
For TreePage the grids are tipically shown in Tabs, so one a time; for this reason the current grid is quite clear there.
There are many actions, mainly available through buttons, that apply preferentially to one grid at a time, as for instance sorting or filtering.