Masjid is an Arabic word which means mosque in the English
language. A masjid is a place where Muslims perform prayers and
worship Allah 
.
What do Muslims do in a Masjid?
In a masjid, Muslims pray five times a day following an Imam
(person who leads the prayer) facing in the direction of the Kaaba in Makkah.
Before each prayer, the Azaan (call to prayer) is said by a Muazzin
(person who calls for prayer). Muslims stand side-by-side to perform
prayers irrespective of their race, wealth or social status.
The Jumah and other special prayers
On every Friday (Jumah) afternoon, a special prayer is held in masajid
(plural of masjid) called The Jumah. Other special prayers are also held
in the masajid such as the Eid prayers and Taraweeh (performed every
night in Ramzaan).
The most holiest masajid
The most holiest masjid is Masjid-ul-Haram (The Sacred Mosque) in Makkah,
Saudi Arabia. This masjid is also called the Kaaba.
The second most holiest masjid is Masjid-ul-Nabawi (The Prophet's Mosque)
in Madina, Saudi Arabia. The original Masjid-ul-Nabawi was built by the
Prophet Muhammad 
. Over time it was expanded and decorated by later
Muslim rulers. The Prophet himself and two of his companions,
Abu Bakr 
and Umar , are buried there.