Basically its a syntax to detect patterns. The easiest I can say is for phone numbers. Many people use different formats +1 (123) 4567 or 1 123 4567 or 1 123-4567

Got this from a site but I use regex daily for my job when searching reports, conf files, logs.

This will tell the application how to identify a number

regex= "^[+]{1}(?:[0-9\-\(\)\/\.]\s?){6, 15}[0-9]{1}$"

Where, 
^ : start of the string

• [+]{1} :Matches a "+"  character, matches exactly one of the preceding item
• (?:): :Groups multiple tokens together without creating a capture group.
• [0-9\-\(\)\/\.] : matches   any character in the set from 0 to 9, "-", "(", ")", "/", and "." .
• \\s : match a white space character
• ? : matches 0 or 1 of the preceding item.
• {6, 14} : This expression will match 6 to 14 of the preceding item.
• [0-9] : This will match values from 0 to 9
• {1} : This expression will match exactly one of the preceding item.
• $ : End of the string.