system
A chat on subreddit /r/pcmasterrace
human
Welding = melting the edges base material itself, allowing the puddles to flow together, then freeze again, two parts fusing and becoming one.

Soldering = heating the base material such that it remains solid, but is hot enough to melt a dissimilar filler material which wets and bonds to the base material. See also brazing.
gpt
I see better now. Thanks.