For the terminology see:
Explanatory Notes - CFTC
esp. section "Old and other futures" (e.g. for "last") and "Supplemental Report" (e.g. for "swap")

The release schedule is as follows:
Release Schedule - CFTC
(That's why I hinted at the lag more than once. Making short-term trades based on CoT is relatively pointless.)

I read those before but have found no explenation there. I've searched the Notes for terms Swap and Last Day with no results and in the Schedule is current release date 4th Sempt, but the CoT report is from 1st. And still I am wondering about the "Crude Oil"...

jirakst 

I read those before but have found no explenation there. I've searched the Notes for terms Swap and Last Day with no results and in the Schedule is current release date 4th Sempt, but the CoT report is from 1st. And still I am wondering about the "Crude Oil"...

If you can't participate in physical delivery, that's "just another Crude symbol" for you - this time settled financially.
https://www.cmegroup.com/trading/energy/crude-oil/brent-crude-oil-last-day_contract_specifications.html

ad "swap": literally from the "Supplemental Report" section
"The commercial category includes positions for entities whose trading predominantly reflects hedging of over-the-counter transactions involving commodity indices—for example, a swap dealer holding long futures positions to hedge a short commodity index exposure opposite institutional traders, such as pension funds."

for a swap primer see: https://en.wikipedia.org/wiki/Swap_%28finance%29

Ok, thank you very much. It really helped me.

jirakst 

Ok, thank you very much. It really helped me.

You're welcome

Two things I will add
1) CFTC is a US agency and as such the CoT report only includes US exchanges. ICE do self report a similar style report to CoT but you have no idea whether the positions they report are additive or offsetting to US reported positions.
2) Looking at just futures ignores a very large piece of the pie. There are all sorts of other instruments that will mirror futures risk that do not necessarily get reported. Also how do they treat spreads that clear AS SPREADS. Do they separate these into their respective individual commodities?
All in all I believe CoT may give you a good picture what Banks/Professionals/CTA's/Hedge Funds etc are all doing but I do not think it gives an accurate picture of what major 'industry' players are doing as it excludes so much of their risk.