To understand what a mosque is in Islam, we need to grasp that Islamic practice and belief is based upon the example and teaching of Muhammad. What determines the function of a mosque — from a religious perspective — is how Muhammad used mosques. The question "What is a mosque?" begs the question "How did Muhammad use mosques?"
But let's consider what a significant contemporary scholar has said on the subject. Yusuf Al-Qaradawi is an influential person. He is no lightweight or fringe-dweller. A trustee of the Oxford University Centre for Islamic Studies, he was named by Foreign Policy Magazine as number 3 in a poll to determine the top 20 public intellectuals in the world today.
In 2006 Al-Qaradawi produced a fatwa (a religious ruling) to answer the question: "Is is permissible to use a mosque for political purposes?" (The Arabic text can be found here.) (Apparently this was a revision of an earlierfatwa, issued in 2001.)
Al-Qaradawi's answer was 'Yes it is,' and included the following remarks:
The mosque at the time of the Messenger of Allah [Muhammad] was the center of the activities of the Muslim community as a whole: it was not just a house of worship and prayer, but included worship, a university for science, a forum for literature, and a parliament for consultation ... it was used by delegations from various places in the Arabian peninsula to meet with the prophet [Muhammad], and it was the place where he gave his sermons and guidance in all religious, social and political aspects of life.
In the life of the prophet there was no distinction between what the people call sacred and secular, or religion and politics: he had no place other than the mosque for politics and other related issues. That established a precedent for his religion. The mosque at the time of the prophet was his propagation center and the headquarters of the state.
This was also the case for his successors, the rightly guided Caliphs: the mosque was their base for all activities political as well as non-political.
... Politics as a science is one of the best disciplines, and as a practice and career it is the most honorable. The surprising thing is that it is politicians, who are totally immersed in it [politics] from the top of their heads to the soles of their feet, who are inquiring if the mosque should embark on and leap into political affairs. Politics in itself is neither vice, nor evil, according to Islam. ... For Muslims it is part of our religion: doctrine and worship constitute a system for the whole of life.
... It must be the role of the mosque to guide the public policy of a nation, raise awareness of critical issues, and reveal its enemies.
From ancient times the mosque has had a role in urging jihadfor the sake of Allah, resisting the enemies of the religion who are invading occupiers. That blessed Intifada in the land of the prophets, Palestine, started from none other than the mosques. Its first call came from the minarets and it was first known as the mosque revolution. The mosque's role in the Afghan jihad, and in every Islamic jihad cannot be denied