What is the @ symbol in Latex used for? I had seen its use in the tables as given below

Question

\multicolumn{1}{|c|}{\multirow{2}{*}{\textbf{\begin{tabular}[c]{@{}c@{}}Attribute\\  No\end{tabular}}}}

Answer 1

From the documentation of the array package:

@{decl.} Suppresses inter-column space and inserts decl. instead.

So here @{} sets the space on both sides of the unique column to 0.