Explain the term 'persons acting in concert' (PACs) with reference to SEBI (Substantial Acquisition of Shares and Takeovers) Regulations, 2011.

'Person Acting in Concert' (PACs) are individual(s)/company(ies) or any other legal entity(ies) who, with a common objective or purpose of acquisition of shares or voting rights in, or exercise of control over the target company, pursuant to an agreement or understanding, formal or informal, directly or indirectly cooperate for acquisition of shares or voting rights in, or exercise of control over the target company. The SEBI (Substantial Acquisition of Shares and Takeovers) Regulations, 2011 define various categories of persons who are deemed to be acting in concert with other persons in the same category, unless the contrary is established.