In terms of the definition of Islamophobia, the term itself came into popular use around 1997 when Runnymede put it out in a publication that they created. I would argue that the concept dates back to the beginning of the faith itself.
The Ontario Human Rights Commission defines Islamophobia as including “racism, stereotypes, prejudice, fear or acts of hostility directed towards individual Muslims”. It's not limited to individual acts of intolerance or racial profiling. It includes a normalized view of Muslims as threats to security, institutions, and society. It also includes one-sided, sweeping negative portrayals of Muslim people, which play a really key role in normalizing and reproducing contemporary forms of this type xenophobia.