Tajug is a pyramidal or pyramid square (i.e. an equilateral square base with a peak) ornament which is usually used for sacred buildings in Southeast Asia including Indonesia, such as mosque or cupola graveyard. It is considered derived from Indian and Chinese architectural style which has history since pre-Islamic era, although there’s also an element of an influence from Indian mosque. The term tajug is also used to refer to mosques or surau (Islamic assembly building) in some regions of Indonesia.

Surau
In some areas of Sumatra and the Malay Peninsula , surau refers to the building of places of worship of Muslims. Its function is almost the same as the mosque as a center of religious activities of society and basic education of Islam. However, since the building is relatively smaller than the mosque, the surau is not usually used for Friday prayers and Ied prayers . In Minangkabau , most surau more devoted as educational institutions because of its location adjacent to the mosque.

The term surau has been known in Minangkabau long before the coming of Islam. AA Navis describes, surau is a gathering place for boys who are already baligh to sleep at night and pursue various sciences and skills. This function did not change after the arrival of Islam, but expanded into a place of worship and the spread of Islamic science. According to Islamic scholar Azyumardi Azra , the position of the surau in Minangkabau is similar to that of a pesantren in Java. However, after independence the existence of surau in Minangkabau gradually subsided because the Islamic educational institutions in Indonesia should be subject to government rules.

In Malaysia, the difference in function between mosque and mosque is not so clear. For administrative purposes, the surau is divided into a large surau and small surau. Although its function is almost the same as the mosque in Indonesia, large surau usually have more complete religious functionaries. However, large surau is generally not intended as an Islamic educational institution. In contrast, small surau is usually also functioned as a place to provide basic religious lessons.

Musala
Musala or Musholla ( Arab : مصلى ) is a place or small house resembling a mosque used as a place of prayer and prayer for Muslims. Musala is also often referred to as surau or langgar .

Its function resembles a mosque , but there are several things that distinguish it from the mosque, namely:

Can not be used for Friday prayers
Can not be used for iktikaf
Sometimes the mushas are the private property of a person
Generally smaller than the mosque

Source From Wikipedia