The review simply means that your return is pending because IRS is verifying information on your tax return. They may contact you before processing your return.
"The most common reason for the IRS to review a tax return is something called the Discriminant Function System (or DIF) score. The IRS uses a computerized scoring model that evaluates your return and gives it a score based on the likelihood that it will need to be changed. To determine this score, the model compares your return to similar returns that the IRS received in past years. A second model, the Unreported Income DIF (or UIDIF) score, rates your return on the probability that you didn’t fully report your income.
Returns that receive a high DIF or UIDIF scores are more likely to be pulled aside for review. Factors that could trigger a high score include having a substantially higher or lower amount of reported income compared to the previous year, claiming excessive deductions for business expenses or leaving a 1099 form off your return.
It is also worth mentioning that the IRS randomly selects a small percentage of tax returns to review. The IRS compares these returns to a sample of “normal” returns in order to see if there are any discrepancies."
What happens when your tax return is flagged for review?: https://smartasset.com/taxes/what-happens-when-your-tax-return-is-flagged-for-review
