How do you define solid and sound?

No, I'm not referring to a literal solid object and actual sound. I'm referring to the common chess terms solid and sound, which are often used to describe openings and positions. But I do wonder: What exactly do they mean? Are they technically the same thing or do they have completely different meanings? Is it good when my opening or position is solid or sound? I tried googling it but it won't give me the answers that I wanted (nor understand what I want in the first place). So what do you guys think are their definitions?

Solid ~ sound. Solid might mean something sound like the Slav or Closed Catalan, but you can be both solid *and* passive, and simultaneously not sound (i.e. making the triangle structure in a Slav or London system but never solving your bad bishop problem). Sound is just something that is objectively okay to play for either side (it could by coincidence be a position that is also solid)

hello marcy

solid means, structually all your pieces are protected. there is no hanging pieces around (hanging pieces are bound to fall eventually). as for playing style, you are not taking risks. all trades you wanna do is equal or better etc. Player is either waiting for a mistake or slowly advancing by following a strategy.

Sound means, as for openings, moves look reasonable. they are mostly okay by the opening principles. No awkward Grob or Orangutan moves.

I hope it helps.

Solid refers to a position without weaknesses, think of solid like a rock.
Sound refers to the anticipated correctness of a series of moves.
Most gambits are unsound.
Positions with a backward or isolated pawn are not solid.

𝑆𝑜𝑙𝑖𝑑..𝐼𝑠 𝑎 𝑓𝑜𝑟𝑚 𝑜𝑓 𝑚𝑎𝑡𝑡𝑒𝑟 𝑎𝑛𝑑 ℎ𝑎𝑠 𝑎 𝑠ℎ𝑎𝑝𝑒. .𝑆𝑂𝑈𝑁𝐷 𝐼𝑆 𝐴 𝐹𝑂𝑅𝑀 𝑂𝐹 𝑊𝐻𝐴𝑇? 𝑚𝑎𝑡𝑡𝑒𝑟 𝑎𝑙𝑠𝑜!! 𝑏𝑢𝑡 𝑖𝑡 𝑡𝑟𝑎𝑣𝑒𝑙𝑠 ... :-) 𝑊𝑒 𝑐𝑎𝑛 𝑜𝑛𝑙𝑦 𝑚𝑒𝑎𝑠𝑢𝑟𝑒 𝑎 𝑠𝑜𝑢𝑛𝑑 𝑏𝑦 𝑖𝑡𝑠 𝐷𝑒𝑐𝑖𝑏𝑒𝑙....

So solid usually means a very sturdy structure with little to no weaknesses while sound means your moves are accuarate, at least that's how I understand it.

Yep, exactly