Code templates are entities that can be instantiated using "code completion". Anything can be added here as long as the first items you type are somewhat unique.
By default most of the common language constructs are available here (always, always_ff, always_latch etc.). Code templates also allow for variables which will be completed in multiple places as they are typed. A good example is the always_ff entry below. Note the variable ${reset_n}. When the user enters the first "reset_n", the item in the first if statement will be updated concurrently.
always_ff @(posedge ${clk} or negedge ${reset_n}) begin
if (!${reset_n}) begin
${flop} <= 1'b0;
end
else begin
${flop} <= ${cursor};
end
end
Code templates can be added to, modified to match your personal preferences or removed in the SVEditor preferences, Window>Preferences>SVEditor>Code Templates. The image below shows the default code templates.