I have $n_1$ packets in group 1 which are numbered from $1$ to $n_1$ and $n_2$ packets in group 2 which are also numbered from $1$ to $n_2$.
These packets in group 1 are sent to a destination. Due to lossy network, we will receive $k_1$ packets, $0 \le k_1 \le n_1$. In same manner, these packets in group 2 are sent to the destination and we can receive $k_2$ packets,$0 \le k_2 \le n_2$
At the destination, we can find some packets have the a same number of two group 1 and 2. What is a technical word to represent the same index number of these packets in the destination? And not same number?
For example, I can receive $k_1=5$ packets in group 1 which have indices as $[2, 3 , 6 , 8, 9]$ and $k_2=4$ packets in group 2 with indices as $[3, 4, 8, 10]$. So the same indices of two group are $[3,8]$. The different indices between group 1 and group 2 are $[2, 6, 9]$ and the different indices between group 2 and group 1 is $[4, 10]$.
The terminology may depend on the context. If having the same indices is a desired property, you may use matching, as suggested by Emil. If, on the contrary, you want to avoid this situation, you may use collision, a term used in particular for hash functions.