New Teradata User - Unfamiliar with SUM(x) OVER () y

Database

New Teradata User - Unfamiliar with SUM(x) OVER () y

Thanks in advance for your responce,

Might you have a moment to fill me in on what this statement is doing:

T0.C7 AS PDE_GDCA_Amt,
sum(T0.C7) over () PDE_GDCA_Amt13

Many thanks!