diff --git a/docs/glossary.md b/docs/glossary.md
index 0cd3acd..df2a1f4 100644
--- a/docs/glossary.md
+++ b/docs/glossary.md
@@ -43,6 +43,10 @@ A downstream consumer node that emits an equity stream, attaching at one of two
 **Avoid:** —
 The dynamically-loadable Rust library form of a project and its nodes, hot-reloaded during authoring; the hot-reload unit is always the project-side cdylib. Frozen to a static artifact for deploy.
 
+### cell
+**Avoid:** —
+The type-erased 64-bit word holding one scalar-base-type value with its kind stripped off (`crates/aura-core/src/cell.rs`): the type lives at the schema/column/port, so a cell is read only by naming it via a branch-free accessor (`i64()`/`f64()`/`bool()`/`ts()`). A `Scalar` is a cell plus its kind tag — the self-describing carrier for the dynamic boundaries — whereas a bare cell is what the SoA hot path reads without a per-value branch.
+
 ### composite
 **Avoid:** —
 A node that wires a sub-graph and exposes one output (a combined signal, or a strategy) — composition is fractal and acyclic. Also names the multi-column stream a node emits: the **record** a producer's `eval` returns, bundling 1..K base scalar columns (e.g. OHLCV), each bound field-wise by a consumer (C7/C8).