In German, compound words (two or more nouns stuck together to make a new word) take the last noun's gender as the new word's gender. Since "Pass" is masculine, any compound word ending in "Pass" will be masculine as well. This can be really handy if you see a compound word you've never seen before, but know the gender of the last noun!
You can read more on that here: http://german.about.com/od/nounsandcases/a/German-Compound-Words.htm
"Pass" is exactly what you would expect it to be in English ie something which allows you to pass through something else. That does not necessarily have to be a port. You can use them for backstage, security, visitors etc., but, as in English, the most commonly used one is the one which is normally shortened for ease of everyday use. That also depends on your everyday context of course!