Notch count is the number of sex partners.
Frequency of sex (amount of times a person has sex) is usually a more valuable metric. It's better to be a lower notch count/higher frequency of sex guy than a high notch count but lower frequency of sex guy. There are a lot of guys who do pickup who have decent notch counts but most of their notches are 1-2 nights only with some gaps in between pickups. A guy with some longer term relationships (6 months-2 years) will have fewer notches due to relationships but likely more frequent sex than a guy who is solely pickup oriented and doesn't typically go beyond 2 months with any individual woman.
In longer term relationships, sex starts out high after the first bang, if the first bang is good enough to get you a repeat bang. It escalates for the first 2-3 months and then has a high plateau level for some amount of time (anywhere from 3 months to about 3 years after).
Very few couples that have been together for 5 or more years are having frequent sex. Frequent sex is a hallmark of 2-5 year long relationships.