Yes, there is a difference between the two terms. Magnetic field is defined as a force field surrounding a magnetic pole that exerts forces on other magnetic poles placed in the field(the area of influence exerted by a magnetic force), it is not a vector quantity and is denoted by the symbol B. However, magnetic field strength, also known as magnetic flux density is a quantitative, vector quantity that is measured in tesla(T) or weber per square metre(Wb/m2). So essentially, magnetic field just refers to the existence of magnetic flux around an object due to its magnetic properties, but magnetic field strength specifically measures how much magnetic flux is in the entire magnetic field. Hope this helps a little.