What is Sikhism?

According to wikipedia.org:

Sikhism is a religion based on the teachings of ten Gurus who lived primarily in 16th and 17th century India. It is one of the world's major religions with over 23 million followers. Sikhism comes from the word Sikh, which in turn comes from its Sanskrit root 'si ya' which means "disciple" or "learner", or from the equivalent Pali word 'sikkha'.

The two core beliefs of Sikhism are:

The belief in one God. The opening sentence of the Sikh scriptures is only two words long, and reflects the base belief of all who adhere to the teachings of the religion: - Ek Onkar
The teachings of the Ten Sikh Gurus (as well as other accepted figures) as enshrined in the Guru Granth Sahib.
The Guru Granth Sahib is a sacred text considered by Sikhs to be their eleventh and final Guru. Sikhism was partly influenced by reform movements in Hinduism, and to a lesser extent, Sufism. Some consider Sikhism to be a syncretic religion, although this is not a widespread belief held by Sikhs. Sikh philosophy is characterised by logic, comprehensiveness, and a "without frills" approach to both spiritual and material concerns. Its theology is marked by simplicity.