Endogenous and exogenous variables:

There are two types of variables in simultaneous equation models: endogenbus and exogenous.

Endogenous  Variables get determined  jointly and interdependently within the model. The endogenous variables are determined by the exogenous variables. Exogenous Variables  are determined outside the model and  independently of the endogenous  variables. These  exogenous  variables determine the  endogenous variables but the endogenous variables cannot  affect  the exogenous variables.
 
Lagged Dependent Variables:

In  a model we  can  include the  lagged value of an endogenous vaiiable alsd. For example,  C_t  is  current  year consumption  and  is  assumed  to  be  an  endogenous variable.  If  we  consider  C_t-1  in  another  equation (which  implies  past  year consumption), then  it is lagged endogenous variable.

Predetermined Variables:

In addition  to the above, often we come across  the term  'predetermined variable'.  It includes  both exogenous variables and the lagged endogenous  variables.