"MARC" stands for Machine Readable Cataloging format. It is a standardized format developed by the Library of Congress for producing machine-readable bibliographic records. It is much more difficult to read than regular tagged data formats, but it can still be imported in much the same way using EndNote’s filters.
Many connection files use the MARC format because it is specified as part of the Z39.50 standard. When creating a new connection file, the Templates and MARC Records portions of the connection file are automatically set up to import standard USMARC (MARC21) data. If you need to customize these parts of the connection file, the instructions in this section would apply.