What's the distinction between a tetrad and a synaptonemal complex in meiosis?
As far as I can tell there is a distinction.

A tetrad refers to the entire group of four chromatids after they have come together for crossing over in Prophase I (synapses).  

A synaptonemal complex as you would expect is formed in synapses.  This is a protein-RNA complex that connects the intervening regions of matched chromosomes in some circumstances - it is not required. Mutated yeast that can not form this complex has still been shown to be able to exchange genetic information. 

In other words, you can have a tetrad without a synaptonemal complex, but not vice versa.