General synonyms:
* Description: A detailed account of something.
* Definition: A precise statement of the meaning of a word or phrase.
* Outline: A general plan or description.
* Detail: A particular aspect or feature.
* Requirement: A necessary or essential condition.
More specific synonyms:
* Blueprint: A detailed plan or drawing.
* Technical specifications: Precise details about a product or process.
* Criteria: Standards or requirements used to judge something.
* Parameters: Limits or boundaries that define a process or system.
* Guidelines: A set of recommendations or rules.
Informal synonyms:
* Breakdown: A detailed analysis of something.
* Lay out: A detailed explanation or presentation.
* Nuts and bolts: The essential details.
* The fine print: The detailed terms and conditions.
The best synonym for "specification" will depend on the specific context and the intended meaning.