what does split string mean in c++ code example

Example 1: split string on character c++

#include <string>       // std::string
#include <sstream>      // std::stringstream

std::stringstream test("this_is_a_test_string");
std::string segment;
std::vector<std::string> seglist;

while(std::getline(test, segment, '_'))
{
   seglist.push_back(segment);
}
// seglist = {"this", "is", "a", "test", "string"};

Example 2: c++ string split

std::vector<std::string> &split(const std::string &s, char delim, std::vector<std::string> &elems) {
    std::stringstream ss(s);
    std::string item;
    while(std::getline(ss, item, delim)) {
        elems.push_back(item);
    }
    return elems;
}