hold back[phrasal verb]
1 a : to stop yourself from doing something
▪ She wanted to introduce herself to him but she held back out of shyness.
b : to make a less than complete effort
▪ She could have beaten him in the race, but she held back and let him win. [=she did not run as fast as she could have so that he would win]
c hold (someone) back : to stop (someone) from doing something
▪ Once he starts talking, there’s no holding him back. [=it’s very hard to get him to stop talking]
2 hold (something) back or hold back (something) a : to not allow (something) to be seen or known by someone
▪ He was unable to hold back his tears. [=to keep from crying]
b : to keep (something)
▪ He held several thousand dollars back in case of an emergency.
c : to delay (something)
▪ The company held back the first shipment of the new product until it was completely ready.
3 hold (someone or something) back or hold back (someone or something) : to stop (someone or something) from moving forward : to stop (someone or something) from advancing to the next level, grade, or stage
▪ She might have been more successful, but bad health held her back. ▪ He was held back [=kept back] in first grade.