system
Given the following post, respond as if you're commenting on Reddit:
human
What is the difference between plasma and ionized gas?
gpt
Nothing really. Although the actual definition can be a bit fuzzy and can depend on the field. Astronomers tend to refer to all plasma as "gas", regardless of how ionised it is. The main difference between plasma and neutral gas is that plasmas are much more affected by magnetic fields, because the particles are charged. But many astronomical effects are dominated by gravity and pressure, and magnetic fields tend to be a secondary consideration, so we tend to think of plasma as just a sub-category of "gas". Other fields will maintain a strong distinction between plasma and gas, to emphasise the importance of magnetism etc.

There's also in-between states, where gas can be partially ionised. How ionised something needs to be to count as a "plasma" is also a bit arbitrary. This is particularly the case for photo-ionisation, where light can ionise specific elements while the gas is still quite cool. But even for thermal ionisation, there is a temperature range where hydrogen gas is ionised but helium isn't. Most of the gas in stars and in interstellar space is 3/4 hydrogen and 1/4 helium, so if it's 75% ionised, is that a plasma, or a partial plasma, or what? It depends on the convention in your field, and generally you can call it what you like as long as you're clear about what you mean.