When they were greeted and hugged, they apologized for the delay. "Se" is a reflexive pronoun. Remember you can omit the pronouns in Spanish and if you don't want to omit you can do it. The sentence would be like that "Cuando ellos se saludaban y se abrazaban, ellos ofrecieron disculpas por su retraso". You can use the reflexive pronoun "Se" with the pronouns "El, Ella, Nosotros and Ellos" El se fracturó un brazo He broke his arm. Ella se miró al espejo She looked in the mirror. A nosotros se nos perdió el reloj. To us lost the watch. Ellos se saludan They greet.