What gallium nitride is
Gallium nitride is a semiconductor: a material that can switch electric current on and off, and that forms the working part of a charger's power circuit. Traditional chargers use silicon for the same job. Gallium nitride can switch faster and handle higher voltages than silicon in the same size, in general terms, which is why it is used in modern chargers.
Those are general properties of the material, not claims about any specific charger described on this site. A charger built with GaN is not automatically better than a charger built with silicon: the design, the components around the semiconductor, and the quality of manufacturing all matter as much as the material. The word GaN describes a material choice, not a performance guarantee.
What GaN does and does not tell you
GaN tells you the material of the power circuit. It does not tell you the charger's power output, its connector type, the laptops it serves, or its quality. Those answers come from the specification for the exact charger type, which is confirmed in the inquiry, not from the material name. A buyer who assumes a power figure from the word GaN alone will assume wrongly.
GaN also does not tell you the charger's safety or compliance: those come from certificates, which are available upon request and confirmed by name for the buyer's market. The interfaces guide explains the connector types, including USB-C interfaces for laptops, and the certificates page explains the confirmation process.
What to ask next
Name the laptop kind and the connector type you need, the quantity you have in mind, and the market you sell into. Ask for the specification for the exact type, the quantity terms, the lead time, and the certificates for your market, by name, with documents attached. The bulk GaN charger inquiry page lists these confirmations.
Before payment, confirm the minimum order quantity and lead time for your order. Certificates are available upon request.