This is the TrendSpec section identifier into which the other Section Identifiers have to be nested see Basic TrendSpec Structure.
The TREND section in a TrendSpec definition does not include any mandatory values, however it has to contain at least one TRACE, SOURCE, XAXIS, and YAXIS section.
If required, you can specify one or more TREND Optional Values. Such optional values can be placed anywhere within the TREND section, as long as they are placed outside of the above subsections.