In Extensible Markup Language (XML) 1.1 (Second Edition) Section 3.1 Start-Tags, End-Tags, and Empty-Element Tags, it's called an "empty-element tag". If you were using XML and needed the formal term, this is the one that I'd use.

However, other markup languages do use other terms for the same concept.

In XHTML™ 1.0 The Extensible HyperText Markup Language (Second Edition) Appendix C HTML Compatibility Guidelines Section C.2 (and later sections), it is called the "minimized tag syntax".

In HTML: The Markup Language (an HTML language reference) Section 4.3 Elements, they are referred to as "void elements".

I've also heard the term "self-closing tag" used. This term is also used in HTML5 A vocabulary and associated APIs for HTML and XHTML Section 8.2.4.43 Self-closing start tag state along with many other sources.

Any of these other terms may be used by someone who is coming from a different background and may not know the term as it's defined in the specification and formal documentations for your particular language.

Mark Byers answer on Stack Overflow to a similar question provides more information about these terms.

In Extensible Markup Language (XML) 1.1 (Second Edition) Section 3.1 Start-Tags, End-Tags, and Empty-Element Tags, it's called an "empty-element tag". If you were using XML and needed the formal term, this is the one that I'd use.

However, other markup languages do use other terms for the same concept.

In XHTML™ 1.0 The Extensible HyperText Markup Language (Second Edition) Appendix C HTML Compatibility Guidelines Section C.2 (and later sections), it is called the "minimized tag syntax".

In HTML: The Markup Language (an HTML language reference) Section 4.3 Elements, they are referred to as "void elements".

I've also heard the term "self-closing tag" used. This term is also used in HTML5 A vocabulary and associated APIs for HTML and XHTML Section 8.2.4.43 Self-closing start tag state along with many other sources.

Any of these other terms may be used by someone who is coming from a different background and may not know the term as it's defined in the specification and formal documentations for your particular language.

Mark Byers answer on Stack Overflow to a similar question provides more information about these terms.

In Extensible Markup Language (XML) 1.1 (Second Edition) Section 3.1 Start-Tags, End-Tags, and Empty-Element Tags, it's called an "empty-element tag". If you were using XML and needed the formal term, this is the one that I'd use.

However, other markup languages do use other terms for the same concept.

In XHTML™ 1.0 The Extensible HyperText Markup Language (Second Edition) Appendix C HTML Compatibility Guidelines Section C.2 (and later sections), it is called the "minimized tag syntax".

In HTML: The Markup Language (an HTML language reference) Section 4.3 Elements, they are referred to as "void elements".

I've also heard the term "self-closing tag" used.

Any of these other terms may be used by someone who is coming from a different background and may not know the term as it's defined in the specification and formal documentations for your particular language.

Mark Byers answer on Stack Overflow to a similar question provides more information about these terms.

In Extensible Markup Language (XML) 1.1 (Second Edition) Section 3.1 Start-Tags, End-Tags, and Empty-Element Tags, it's called an "empty-element tag". If you were using XML and needed the formal term, this is the one that I'd use.

However, other markup languages do use other terms for the same concept.

In XHTML™ 1.0 The Extensible HyperText Markup Language (Second Edition) Appendix C HTML Compatibility Guidelines Section C.2 (and later sections), it is called the "minimized tag syntax".

In HTML: The Markup Language (an HTML language reference) Section 4.3 Elements, they are referred to as "void elements".

I've also heard the term "self-closing tag" used. This term is also used in HTML5 A vocabulary and associated APIs for HTML and XHTML Section 8.2.4.43 Self-closing start tag state along with many other sources.

Any of these other terms may be used by someone who is coming from a different background and may not know the term as it's defined in the specification and formal documentations for your particular language.

Mark Byers answer on Stack Overflow to a similar question provides more information about these terms.