That's a hobby servo, from a dubious source. It's not a technical device marketed to technical people, so don't expect a datasheet that has technical, verifiable specifications.
There are hobby servos that come with specifications, and sometimes they even meet their claims. If you want to buy one and have it Just Work, start with a company that lists said specifications, and that has a reputation for standing behind their work.
What does the 60KG mean?
It's very possibly a model name. Servos produce torque, and a kilogram is a unit of mass. Even when misused as a unit of force (i.e., $\mathrm {kg} \cdot 9.8\mathrm{m/s}$ it's still not a torque.
I assume that 8.4V High Voltage is the amount of power it needs to run at full potential.
If it were a technical specification, $\mathrm{8.4V}$ would be enough. "High voltage" just indicates that it uses more than the old-style 4-cell Nicad pack (4.8V nominal, essentially between 4V and 5V).
Assuming that it's a quality part, "$\mathrm{8.4V}$" almost certainly means that it's designed to run off of two unregulated Lithium-Polymer batteries in series. But you're buying a no-name part from an unreliable vendor.
Large torque means it can lift a lot of weight, but how much?
"Large" is a marketing word, designed to make stop thinking long enough to buy the thing. A real specification would list a torque in inch-pounds or Newton-meters. A better specification would have short-term torque and holding torque (but you won't find that in a hobby servo from any source).
"Large" torque means it can twist hard. Force = torque / diameter, so large torque means nothing in terms of how much weight it can lift unless you specify a lever arm.
