LTS means long-term support. The acronym is often used to mark Node.js release lines that will be maintained and supported for an extended period. There are two separate kinds of LTS releases: Active and Maintenance. The Active release line often gets new features and other improvements beside security patches and bug fixes, and the Maintenance only gets the latter. It should be preferred to update to an Active release from Maintenance when possible.
Linux also has LTS versions of the kernel. Long term support is a feature where, unlike standard releases which are supported for a limited time and cease receiving updates unless patched by users manually, the LTS release receives security patches and bug fixes until it reaches its end-of-life. This allows systems using this kernel version to continue being used safely without having to apply additional patches manually.
An LTS release is ideal for use in production environments where stability is paramount and upgrading to new versions is often disruptive. For development or test environments, using the latest standard release is often more desirable as it contains the latest features and improvements.