cell biology - 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.