Various Genetic Loads and their Definitions
The genetic load is a population construct, a way of quantifying the fitness reduction in a population due deviations from the optimal genotype.

One type of load comprises all the others, namely genetic load.


  
  Genetic load is just the loss of mean fitness relative to the ideal fitness.
  


You forgot to include substitution load in your list, but otherwise I think you included all the main ones.


  
  Substitution load is the total loss of mean fitness caused because favorable alleles substitute gradually by selection rather than
  instantaneously.
  


As for the ones you mentioned:


  
  Mutational load is just the accumulation of deleterious alleles in a population.
  Segregating load is the decrease in fitness in a population due to homozygotes being less fit.
  Drift load is the fixation of deleterious alleles due to small population size. The smaller the population, the greater the risk of
  this happening.
  Lag load is the loss of fitness due to a change in environment.
  


Another type, mentioned by rg255:


  
  Gender load, which is the deviation from the optimum due to an allele drifting back and forth because the version that is optimal in one sex is not the one that is optimal in another.