An insider ring is a group of people who collaborate to profit from insider trading. An insider ring would typically include at least one person who has regular access to price sensitive information, and others who have the money to trade on the information.
Because the insider passes information on to other members of the ring, rather than trading themselves, it becomes harder for regulators to prove that insider trading takes place — especially if there is not obvious connection between the members of the ring. The information may pass through several people, so the chain can be very hard to trace.
In return for the information, the insider who passes information along obviously needs some share of the profits. Effectively, money laundering is needed to disguise the transactions.
A common position for the insider leaking the information would be in M & A, where there is a regular flow of price sensitive information. Sometimes, the information can be originate well away from the issuer whose securities are affected. For example, early knowledge of the changes in the recommendations made by influential sell side analysts.
The person at the end of the chain is most likely to be a well funded short term trader, such as a hedge fund managers, a proprietary trader or a day trader. The trades themselves need to performed in a way that does not attract suspicion. Trader who regularly take risky positions are likely to get away with insider trading. They also sometimes limit the size of their trades — this at least indicates the insider trading laws have some effect.