How Can I Understand this Vendor-Specific SMART Attribute?

I can't phrase it better than Wikipedia:

The term "S.M.A.R.T." refers only to a signaling method between internal disk drive electromechanical sensors and the host computer. Because of this the specifications of S.M.A.R.T. are entirely vendor specific and, while many of these attributes have been standardized between drive vendors, others remain vendor-specific.
...
issues remain due to attributes intentionally left undocumented to the public in order to differentiate models between manufacturers
...
manufacturers do not necessarily agree on precise attribute definitions and measurement units
...

So your best bet to understand all attributes of a specific disk and their implication is to use the vendor supplied tool, such as for instance the Western Digital Dashboard

Generic tools, although they can read all the supplied S.M.A.R.T. attributes, may not have the complete picture to interpret non-standard attributes in a meaningful way; displaying those as Vendor Specific is technically correct.

https://kb.acronis.com/content/9110 ;

Attribute ID: 10 (0x0A)
Hard drives, supporting this attribute: Samsung, Seagate, IBM (Hitachi), Fujitsu, Maxtor, Western Digital
Description: Spin Retry Count S.M.A.R.T. parameter indicates the count of retry of spin start attempts. This attribute stores a total count of the spin start attempts to reach the fully operational speed (under the condition that the first attempt was unsuccessful). Spin attempts are counted for the entire hard drive's lifetime so far.