| XMM-Newton |
X-ray Multi-Mirror Mission Newton |
| XRISM |
X-ray Imaging and Spectroscopy Mission |
| XSD |
X-ray Science Division |
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| Y4Y |
You for Youth (unable to verify 10/23) |
| YALI |
Young African Leaders Initiative |
| YARH |
Youth/Young Adults with Child Welfare Involvement At-Risk of Homelessness |
| YCC |
Youth Conservation Corps (older link archive) |
| YCR |
Yellowstone Center for Resources |
| YE4C |
Youth Engaged 4 Change |
| YFC |
Institute of Youth, Family, and Community (changed to IYFC) |
| YHDP |
Youth Homelessness Demonstration Project |
| YM |
Youth Mentoring (older link archive) |
| YMSM |
Young Men Who Have Sex With Men Project |
| YRBSS |
Youth Risk Behavior Surveillance System |
| YRC |
Young Readers Center |
| YRTC |
Youth Regional Treatment Centers |
| YSS |
Year of the Solar System (unable to verify 3/16) |
| YTS |
Youth Tobacco Survey |
| YVPCs |
National Centers of Excellence in Youth Violence Prevention (older link archive) |
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|
| ZBOT-NC |
Zero Boil-Off Tank-Non-Condensable |
| ZBP |
Zip Code Business Patterns |
| ZCTA |
ZIP Code Tabulation Areas (older link archive) |
| ZIP (Code) |
Zone Improvement Plan |
| ZSI |
Zero Suicide Initiative |
