What is a variance component model?

I was wondering what the definition of a variance component model is? I searched it online, and found it often appears with mixed-effect models, but couldn't understand what it is, and how it is different from and related to mixed-effect models.

Variance component models "estimate the variability accounted for by each level of the hierarchy". They can refer to mixed (fixed and random) intercept models, in the form of $$y_{ij}=\beta_0+u_i+\epsilon_{ij},$$ where $u_i∼N(0,\sigma_u^2),\epsilon_{ij}∼N(0,\sigma_{\epsilon}^2)$ are the two variance components.