Can you explain what the '+' symbol means in the context of regular expressions?

In regular expressions, the + symbol means "one or more" repetitions of the previous character or group. That is, it requires that the element to the left of + appears at least once in a row.

For example, the expression a+ matches strings with one or more 'a' letters: "a", "aa", "aaa", etc.

Example in Python:

import re
pattern = re.compile(r'a+')
print(pattern.findall('caaat aaa bat'))  # Outputs ['aaa', 'aaa']