The paisa (Bengali: পয়সা, Hindi: पैसा, Urdu: پیسہ) is a monetary unit in several countries; cognate terms include poisha (Bengali: পয়সা, in Bangladesh) and baisa (Arabic: بيسة, in Oman). In India, Nepal and Pakistan, the paisa currently equals 1⁄100 of a rupee. In Bangladesh, the poisha equals 1⁄100 of a Bangladeshi taka. In Oman, the baisa equals 1⁄1000 of an Omani rial.
The word paisa is from Hindi & Urdu paisā, a quarter-anna coin, ultimately from Sanskrit term padāṁśa meaning 'quarter part', from pada 'foot or quarter' and aṁśa 'part'.
Until the 1950s in India and Pakistan (and before 1947 in British India), the paisa was equivalent to 3 pies, ¼ of an anna, or 1⁄64 of a rupee. After the transition from a non-decimal currency to a decimal currency, the paisa was known as a naya paisa ("new paisa") for a few years.
General usage of the term 
In Hindi, Afghan Persian, and other languages, the word paisa often means money or cash. Medieval trade routes that spanned the Arabian Sea between India, the Arab regions and East Africa spread the usage of Indian and Arabic currency terms across these areas. The word pesa as a reference to money in East African languages such as Swahili dates from that period. An example of this usage is the modern day Kenyan mobile-phone based money transfer service M-Pesa (which stands for mobile pesa or mobile money)
Example currency 
Here are examples of paisa:
100 Omani baisa note (reverse)