Sequential SS: The sum of squares for a model term in ANOVA, which partitions out the variation due to the term after accounting for variation due to earlier terms in the model hierarchy. Sequential SS (often referred to as Type-I SS) are suitable for orthogonal designs; non-orthogonal designs use adjusted SS.

Doncaster, C. P. & Davey, A. J. H. (2007) Analysis of Variance and Covariance: How to Choose and Construct Models for the Life Sciences. Cambridge: Cambridge University Press.

http://www.southampton.ac.uk/~cpd/anovas/datasets/