what does concatenate mean in java code example

Example 1: java concatenate strings

public class Concat {
    String cat(String a, String b) {
        a += b;
        return a;
    }
}

Example 2: java best way to concatenate strings

// StringBuilder
String stringBuilderConcat = new StringBuilder()
    .append(greeting)
    .append(" ")
    .append(person)
    .append("! Welcome to the ")
    .append(location)
    .append("!")
    .build();