The most common and most likely answer to this crossword clue is the 6 letter word SCHEMA
I've seen this crossword clue in The Guardian
S
C
H
E
M
A
More clues leading to the result SCHEMA
- Plan that is borderline acceptable initiated
- Conservative overwhelmed by shame messed up plan
- Plan after-school English qualification
- Plan to get English degree after school
- Outline he sculptured briefly on skirt and angora top
- Plan‘s south roughly around bottom edge?
- Map of border in Southern California
- Nietzsche managed to conceal the outline
- Layout of South Carolina border area
- Scam, eh? Worried? Make a plan!
Buddy explains!

The straight part
We know that "Plan" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case plan = schema.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SCHEMA mean?
SCHEMA noun- An outline or image universally applicable to a general conception, under which it is likely to be presented to the mind (for example, a body schema).
- A formal description of the structure of a database: the names of the tables, the names of the columns of each table, and the data type and other attributes of each column.
- (markup languages) A formal description of data, data types, and data file structures, such as XML schemas for XML files.
- A formula in the metalanguage of an axiomatic system, in which one or more schematic variables appear, which stand for any term or subformula of the system, which may or may not be required to satisfy certain conditions.
- A monastic habit in the Greek Orthodox Church.