[racket] Regexp-match question: ? means what, or .*? means what...

Regexp-match question: ? means what, or .*? means what...

;This I understand:
;To return pattern and everything to left of first instance of pattern,
use: [^<pattern>]*<pattern> ;where ^ means 'not'; example:
(car (regexp-match* #rx"[^/]*/" "12/4/6")) ; => "12/"

;This I do not understand:
;To return pattern and everything left of first instance of pattern, use:
.*?<pattern> inside #rx""; where ? means _______; or where .*? means
______________; example:
(car (regexp-match* #rx".*?/" "12/4/6")) ; => "12/"

Can you replace my ________ with some words?
Any comments are very much appreciated.
Thanks.
Don Green
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