I am reading (also learning) a paper using structural equation modeling (SEM) as their analysis method. Their analysis was constructed by using a correlation matrix and asymptotic variances. They follow the two-step method (Anderson and Gerbing, 1988) with the baseline model being constructed first to confirm the stability of the latent variables. I am still confused about the term "baseline model" here. The author proposed a casual model (all paths), which is later examined. However, I cannot find they defined "baseline model". What is the baseline model here?

Thanks