Quantifiers or Repetition of Characters - RegEX

0 or more *
1 or more +

Example
\d* to match any number of digits,
a+ (one or more a's),
[abc]+ (one or more of any a, b, or c character)

z{3,5}
Find any z with three to five repeats

z{5},
Find any z with five repeats

ab?c
matches strings with abc or ac
because b is optional