A more thorough explanation:

An integrated pension plan is a type of retirement plan that takes into account the Social Security benefits an employee will receive when determining their total retirement benefit. This means that the employer can reduce the amount of their pension benefit based on the amount of Social Security benefits the employee will receive.

Congress first recognized integration in the Internal Revenue Code Section 401(a) by noting that a pension plan is not discriminatory merely because it excludes employees whose pay qualifies for Social Security benefits. By enacting the Employment Retirement Income Security Act (ERISA), Congress approved the existing provision by allowing integration based on three factors: the employer’s contribution to other benefit funds, whether the funds are meant to be used by the general public, and whether the benefits supplied correspond with the pension plans.

For example, let's say an employee is eligible for a pension benefit of $1,000 per month and is also eligible for Social Security benefits of $500 per month. If the employer has an integrated pension plan, they may reduce the employee's pension benefit to $500 per month, taking into account the Social Security benefits the employee will receive.

However, ERISA prohibits an integrated pension plan from lowering an employee's benefits if there is an increase in their Social Security benefit level after ERISA's enactment date. This ensures that employees are not unfairly penalized for changes in Social Security benefits.

Overall, an integrated pension plan can be a useful tool for employers to provide retirement benefits to their employees while taking into account other sources of retirement income, such as Social Security benefits.