Difference between Bayesian Networks and Dynamic Bayesian Networks
A DBN means that your model is replicated over each time discrete time step t, called slice. Variables of each slice can be connected together, as well a from previous slice to a latter slice (in this precise direction only). The probability tables and links remain the same in each slice if the model is stationary, which is the default case (otherwise they are a function of t).

In a 2TBN (2-step Timeslice Bayesian Network), there are links only between the previous and current slices.

For more information c.f. section 3.2 of http://journal.frontiersin.org/article/10.3389/fncom.2014.00131/full