The phrase "particular specialism" refers to a specific area of expertise or skill that someone has. It means that the person is knowledgeable and skilled in a specific field or subject, rather than being a generalist. Full definition
Charmaine is accredited by Resolution as a specialist family lawyer with particular specialisms in Advanced Financial Provision II and Child Abduction. (wedlakebell.com)
Broad expertise with particular specialisms in retail and consumer, financial services, industrials and digital matters. (addleshawgoddard.com)
But many partners in law firms run essentially small «independent» businesses in their practice areas, directly accountable to their clients, with their own particular specialism. (lawyer-monthly.com)