By Roger Hardy BBC Middle East analyst

Osama Bin Laden, named by US officials as the main suspect in the 11 September attacks against America, is Saudi-born and a Wahhabi.

Many people are accordingly asking about the character of "Wahhabism" and debating whether it is an inherently radical form of Islam.

The term "Wahhabi" is often used very freely.

The Russian media, for example, use it as a term of abuse for Muslim activists in Central Asia and the Caucasus, as well as in Russia itself - rather as the Western media use the vague and derogatory term "Islamic fundamentalism".

In fact, the term is properly used to describe an Islamic revivalist movement which sprang up in the Arabian peninsula in the 18th century.

Like many revivalists in the course of Muslim history, Muhammad Ibn Abdul-Wahhab, the founder of the movement, felt that the local practice of Islam had lost its original purity.

Wahhabi rules

Saudis themselves do not use the term "Wahhabi", preferring to call themselves Unitarians - believers in one indivisible deity.

Bin Laden supporters have been demonstrating in Pakistan

The modern Saudi state is founded on the 18th-century alliance between the Wahhabi religious movement and the House of Saud - the family that has ruled the Saudi kingdom since its creation in the 1930s.

In daily life, the Saudi religious establishment - the ulema - have imposed strict segregation of the sexes, an absolute prohibition of the sale and consumption of alcohol, a ban on women driving and many other social restrictions.

The rules are enforced by the "mutawa", or religious police, who patrol the streets and shopping centres on the look-out for anyone breaking the rules.

Taleban version

There are some similarities between the Saudi interpretation of Islam and that of the ruling Taleban movement in Afghanistan.

The Taleban, too, represent an unusually strict form of Sunni Islam - and restrictions on women, for example, are even tighter than in Saudi Arabia.

But the Taleban are not Wahhabis.

They belong to what is known as the Deobandi movement, named after the small town of Deoband in the Indian Himalayas.

It was here that the movement was founded, in the 1860s, during the period of British rule in India.

Over time, the movement has become a broad umbrella, including in its ranks Muslims who wish to remain aloof from politics - and others, like the Taleban, who are politically militant.

It would be wrong to see either Bin Laden or the Taleban as typical of modern Sunni movements.

They represent a radical fringe, rather than the Sunni mainstream.