This is a 'lay person' definition but......I too have always had eczema (born scratching) and lots of skin issues. I believe the difference I've noticed between the two is that eczema doesn't create 'raised patches' of skin. A friend with plaque psoriasis had large, gray scaly patches on his skin (sometimes red) whereas eczema is more of a flat rash? All that said, dermatologist seem to spot the difference pretty easily between the two. Psorasis can be associated with other conditions like heart disease and can be a sign of those underlying conditions and eczema is a huge nuisance brought on by histamine production I the body and on the skin.
There are thousands of skin rashes (literally) and even dermatologists can be stumped at times but both psoriasis and eczema are pretty common complaints so doctors do a bit better pinpointing those.