Structural Equation Modelling (SEM) is a widely used technique in statistics to primarily study relationships based on structures. It encompasses various models involving mathematics, statistical procedures etc. This technique is known to be extremely effective when it comes to measuring latent constructs.
Many of us might be familiar with concepts like Multiple Regression Analysis and Factor Analysis, this in simple term, is a combination of these techniques. It is, in fact, a mere extension of General Linear Model. You can test a bunch of regression techniques at the same time.