Short answer. It's the official name. Rule 1, Section 1 of the Rules of Civil Procedure provides that these Rules shall be known and cited as the Rules of Court, so the short title used throughout Philippine legal practice is the rules' own designated citation, not informal shorthand.
What the law says
These Rules shall be known and cited as the Rules of Court.
Rule 1, Section 1 — Title of the Rules. Read the full provision →
What the section does
It is a one-sentence provision fixing the official short title: these Rules shall be known and cited as the Rules of Court. Nothing more is packed into the section — no substantive rule of procedure, no exception, no qualification. Its entire function is naming, and it performs that naming job by direct rule rather than by describing a practice that simply grew up informally over time among courts and practitioners.
Why a title provision exists at all
Procedural rules are cited constantly in pleadings, motions, and decisions, so fixing the exact name to be used avoids inconsistent references to the same body of rules across the legal system. Without a designated short title, courts, lawyers, and litigants might refer to the same body of procedural law by several different informal names, creating confusion about exactly which set of provisions a citation is actually pointing to. Naming the whole body once, at the very outset, heads that problem off entirely.
What "these Rules" actually covers
The designation applies to the whole body of rules governing procedure before Philippine courts, of which the Rules of Civil Procedure, opened by this very section, form one part alongside the rules on criminal procedure, evidence, and special proceedings. Each of those component parts is still promulgated and amended as part of the same overall body, so a citation to "the Rules of Court" can be understood to reach any of them, not merely the civil procedure rules where this particular section happens to appear.
Why this matters practically
When a contract, statute, or court order refers generically to "the Rules of Court," it is invoking this same officially titled body of procedural law fixed by this section, not some separate or informal reference. A lawyer citing "the Rules of Court" in a pleading is using the rules' own designated name, not an abbreviation they invented, which is why the citation is treated as precise rather than colloquial shorthand. It also means a challenge to a document's validity cannot rest on the argument that "the Rules of Court" is merely informal or colloquial usage, since Section 1 itself confirms that the phrase is the rules' own official, self-designated citation.