See the license under which the third-party work is available. There typically is a clause that mandates any redistribution to include specific copyright notices. The exact wording is different in each license, but the copyright notices typically follow the form "Copyright (c) <year(s)> <owner>". See below for some simple examples.
The reason why the NOTICE shouldn't contain much extra text is that our license makes a strict requirement that any derivative works contain those notices. Including text like "this dependency is used for X" or "this dependency is licensed under Y" may be troublesome as the derivative work may well be heavily refactored or relicensed. So, keep the NOTICE file clean and put any extra explanations to the README or some other similar place.
1) The Apache License version 2.0
If the Work includes a "NOTICE" text file as part of its distribution, then any Derivative Works
that You distribute must include a readable copy of the attribution notices contained within
such NOTICE file, excluding those notices that do not pertain to any part of the Derivative Works,
Include the relevant copyright notices found in the NOTICE file.
2) BSD license:
Copyright (c) <YEAR>, <OWNER>
All rights reserved.
Redistributions in binary form must reproduce the above copyright notice, this list of conditions
and the following disclaimer in the documentation and/or other materials provided with the distribution.
Include the "Copyright (c) <YEAR>, <OWNER>" line. Possibly also the "All rights reserved." line?
3) The MIT license:
Copyright (c) <year> <copyright holders>
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
Include the "Copyright (c) <year> <copyright holders>" line.