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terminology.md

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 # Canonical Definitions for MEDS Terminology Elements
 
-#### "vocabulary index" or "code index"
+In addition to those terms defined in the
+[official MEDS Schema](https://github.com/Medical-Event-Data-Standard/meds), we define the following terms for
+use in MEDS-transforms:
+
+#### _vocabulary index_ or _code index_
 
 The integer index (starting from 0, which will always correspond to an `"UNK"` vocabulary element) that
 uniquely identifies where in the ordered list of vocabulary elements a given element is located. This will be
 used as an integral or positional encoding of the vocabulary element for things like embedding matrices,
 output layer logit identification, etc.
+
+#### A _measurement_ or _patient measurement_ or _observation_
+
+A single measurable quantity observed about the patient during their care. These observations can take on many
+forms, such as observing a diagnostic code being applied to the patient, observing a patient's admission or
+transfer from one unit to another, observing a laboratory test result, but always correspond to a single
+measureable unit about a single patient. They are encoded in MEDS datasets as a single row in the main MEDS
+schema.
+
+#### An _event_ or _patient event_
+
+All observations about a patient that occur at a unique timestamp (within the level of temporal granularity in
+the MEDS dataset).
+
+#### An _event index_
+
+For a given patient, when the set of unique timestamps (including the null timestamp, which corresponds to all
+static observations) are sorted in ascending order, the event index is the integer index of the timestamp in
+this sorted list.
+
+#### A _static measurement_
+
+A _static_ measurement is one that occurs without a source timestamp being recorded in the raw dataset **and**
+that can be interpreted as being applicable to the patient at any point in time during their care.
+
+#### A _time-derived measurement_
+
+Measurements that are time-varying, but can be computed deterministically in advance using only the timestamp
+at which a measurement occurs and the patient's static or historical data, such as the patient's age or the
+season of the year in which a measurement occurs. These measurements warrant special consideration as they are
+often valuable covariates but not targets of prediction in ML use cases.
+
+#### A _dynamic measurement_
+
+Measurements that are time-varying and cannot be computed deterministically in advance. The vast majority of
+the data in a MEDS dataset will be dynamic measurements.