what does s1 xt mean?

I have checked market only at the closing today.

After closing it has S1 XT 2,537,900 transaction.
Does anyone know S1 XT meaning/

I also have checked today's OST trades and
its SP hit intra day high of 88.5 and retreated at the closing.

It looks like something artifical trade.
Not sure pumping on certain purpose or something is going on behind scene or accumulating by bigger players.

Chart is very good shape atm. But recent run could call profit taking. As for me I did taking some profit today just in case to buy at lower price or buy more again after confirming continued buying momentum.

Regards,