The nisba (النسبة) refers to a class of adjectives that generally indicate origin or affiliation, or most commonly, nationality. To form a nisba, the definite-article 'alif-laam(ال) is removed, as are any of the endings 'alif(ا), yaay-'alif (يا) or taa' marbuuTa (ة). After this is done, the nisba ending is added, and the new nisba adjective is formed. The nisba endings are -يِّ (-iyy) when modifying a masculine noun, and -يِّة (iyya) for feminine. In this way, you can form nationalities:
- مسر --> مسةي/ة...(miSr --> miSriyy/a) Egyptian
- ليبيا --> ليبي/ة...(liibyaa --> liibiyy/a) Lybian
- الصن --> صني/ة...(aS-Sin --> Siniyy/a) Chinese
- المكسيك --> مكسيكية...(al-maksiik --> maksiikiyy/a) Mexican
The nisba can also be used other ways than nationality, such as in the sentence انا طالب جامعي (anaa Taalib jaamiciyy) means 'I am a University Student'.
Also, like many adjectives in Arabic, the nisba adjectives can be used as a noun, as in the sentence هذه لبنانية جميلة (haadhihi lubnaaniyya jamiila) 'That Lebanese chick is hot'.
Overall, the nisba is a pretty cool little grammatical feature. Interstingly enough, this is the reason why in English we use 'i' as a suffix for some Arabic-speaking nationalities, like Saudi, Iraqi, Qatari, etc. and some other nations heavily influenced by Arabic culture, such as Pakistani, Azeri, Somali, etc. | 
