 <p>If you follow through the <a href="https://referencesource.microsoft.com/#System.Xml/System/Xml/Serialization/XmlSerializer.cs,292c7197dcb706a1" rel="nofollow">reference source</a> you end up <a href="https://referencesource.microsoft.com/#System.Xml/System/Xml/Serialization/Compilation.cs,661" rel="nofollow">here</a>.</p> <p>It would seem it's the directory that <code>XmlSerializer</code> will put the serializer assembly it generates. </p> <p>If not specified (which is the case with all other overloads), it uses the <a href="https://msdn.microsoft.com/en-us/library/system.xml.serialization.configuration.xmlserializersection.tempfileslocation(v=vs.110).aspx" rel="nofollow"><code>TempFilesLocation</code></a> which can be configured <a href="http://stackoverflow.com/questions/3302752/changing-where-xmlserializer-outputs-temporary-assemblies">per this related question</a>.</p>