All strings that contain no run of a's of length greater than two for $\Sigma = \{a,b,c\}$
The $+$ sign stands for union, but you got the order of operations wrong. Your regular expression is the sum of $(b+c)^*$ and
$$ (b+c)^*((a+aa)(b+c)^+)^*(a+aa)(b+c)^*. $$