Magnetic flux density is also known as magnetic induction.
When a magnetic material is placed in an external magnetic field then material gets magnetized. Such magnetism produced in the material is called induced magnetism and the phenomenon is called is called magnetic induction
It is also defined as the number of magnetic lines of force inside a magnetized material crossing unit area normal to their direction.
Its S.I. units are weber per square meter.
Reference: This article is referred from my authored book “electrical engineering materials” having ISBN- 978-81-272-5069-0