Verilog is a Hardware Description Language (HDL) used to model digital logic. The values of signals can be written out to a Value Change Dump (VCD) file while simulating logic circuits. The syntax of the VCD *text file* is described in the documentation of the IEEE standard for Verilog, ...
top.sv or check.sv is a typical file name. These files can be linked to testbench, adder, simplified, counter, verilog, design, system and clock. The remaining 70% of all SV files are files with no common format, the following 11 formats can be found: Source, timescale, MPQ and ...