I've dummy coded a variable in my research. In my 'measures' section I say

"type of chocolate was measured using 4 categories, which for the purposes of analysis were dummy coded, using 'galaxy' as a reference category".

My supervisor has written "need to explain what this means" next to this sentence.

Now I think that my examiners either should know what this means, or should go and read a book to find out!

Am I being unreasonable, or should I try and explain what this means (My sup is rubbish at stats, so not sure on this one!)

I generally thought like you with my thesis i.e. I can't explain everything that isn't directly about my thesis and could be considered common knowledge. But I haven't gone through my viva yet so who knows what my examiners will think.

On the other hand it would only take a line to say what dummy codings is. I generally did put extra explainations in if my supervisors suggested it - I didn't want to end up in a situation where I hadn't included things and then I got criticised for it.

Same here, I add all of my sups suggestions. I had a table for dummy coding if that helps...

I think what you've said is pretty conventional - the only thing I can think of is if your variable is categorical rather than ordinal it might be better to report the 4 categories as it's not like they're on a standard scale. Maybe you also need to justify why it's Galaxy, not Cadbury, that's the reference category?