What is Umrah

the non-mandatory lesser pilgrimage made by Muslims to Mecca, which may be performed at any time of the year.

noun: umrah; plural noun: umrahs
Arabic ῾umra

The ʿUmrah (Arabic: عمرة‎‎) is a pilgrimage to Mecca, Saudi Arabia, performed by Muslims that can be undertaken at any time of the year, in contrast to the Hajj. In Arabic, Umrah means “to visit a populated place.” In the Sharia, Umrah means to perform Tawaf round the Kaaba and Sa’i between Al-Safa and Al-Marwah, after assuming Ihram (a sacred state), either from a Miqat like Zu ‘l-Hulafa, Juhfa, Qarnu ‘l-Manāzil, Yalamlam, Zāt-i-‘Irq, Ibrahīm Mursīa, or a place in Hill. It is sometimes called the ‘minor pilgrimage’ or ‘lesser pilgrimage’, the Hajj being the ‘major’ pilgrimage and which is compulsory for every able-bodied Muslim who can afford it. The Umrah is not compulsory but highly recommended.

Difference between Hajj and Umrah

Both are Islamic pilgrimages, the main difference is their level of importance and the method of observance.
Hajj is one of the five pillars of Islam. It is obligatory for every Muslim once in their lifetime, provided they are physically fit and financially capable.
Hajj is performed during a designated Islamic month. However, Umrah can be performed at any time.
Both seem similar in the start. Umrah can be performed in less than a few hours while Hajj is more time consuming, and involves more rituals.