A Roth IRA is post-tax. You pay tax on the income you earn this year, put it in the Roth IRA, and then it grows with no further taxes due on the gains. With a pre-tax traditional IRA, you deduct your contributions from your income in the year you contribute, then the full amount you withdraw counts as taxable income in the year you withdraw it.
There are income limitations for each of these. As a single person you can only contribute the full amount to a pre-tax traditional IRA when your MAGI is under $61k. You can only contribute the full amount to a Roth IRA when your MAGI is under $117k. For this purpose your MAGI would include your full salary and bonus minus your pre-tax 401(k) contributions and some other deductions.
For people over both of these limits, there's another option, the "backdoor Roth IRA." There's no income limit for putting after-tax money in a traditional IRA, and this money can be converted to Roth IRA at any time by paying tax on it. The complication is that any Roth conversions from a traditional IRA are pro-rated between pre-tax and post-tax money. If you already have some money in a pre-tax IRA, you'll pay tax on that pre-tax money if you make Roth conversion. On the other hand, if 100% of your traditional IRA money is post-tax, that means you can convert it all to Roth tax-free and likely never owe tax on that chunk of your stash again. It's rightfully called a "back door" because it essentially allows you to make Roth IRA contributions when your income is too high to do it otherwise.
Since you are pretty close to the Roth IRA limit I might suggest you consider keeping your money in a 401(k) to leave the backdoor Roth IRA option open in future years if your income gets too high to make regular Roth IRA contributions.