IB Computer Science Glossary — Key Terms & Command Words (2027 Syllabus)
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Free reference · IB Diploma · Computer Science · 2027 syllabus

IB Computer Science Glossary

Every key term across the IB Diploma Computer Science 2027 syllabus, organized by unit, plus the IB command terms that decide how much detail an exam answer needs. Free to use — bookmark this page for quick lookups while revising.

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IB command terms

What each instruction word expects in your answer — the single biggest reason marks are lost is answering a "describe" question with a "state"-level response.

Define — give the precise meaning of a word or concept.
State — give a specific name, value or brief answer — no explanation needed.
Identify — pick out an answer from a number of possibilities.
Outline — give a brief, structured summary or overview.
Describe — give a detailed, step-by-step account.
Explain — give a detailed account that includes reasons or causes.
Distinguish — make the differences between two or more items clear.
Compare — give an account of the similarities between two or more items.
Construct — display information in a logical/diagrammatic form, or build the code/query/diagram asked for.
Discuss — give a balanced review that includes a range of arguments or factors.
Evaluate — weigh up strengths and limitations to reach a conclusion.
Suggest — propose a possible answer, solution or hypothesis.

Glossary by unit

B1 · Computational Thinking
Abstraction — hiding unnecessary detail to focus on what matters for the problem.
Decomposition — breaking a complex problem into smaller, manageable parts.
Pattern recognition — spotting similarities or trends across a problem to reuse a known solution.
Success criteria — specific, testable statements that define when a solution counts as working.
B2 · Programming
Iteration — repeating a block of code, using a counted or conditional loop.
Selection — choosing between code paths based on a condition (if/elif/else).
Stack — a LIFO (last-in, first-out) structure — only push/pop the top item.
Queue — a FIFO (first-in, first-out) structure — items leave in the order they arrived.
Big-O notation — a way of describing how an algorithm's run time grows as input size grows.
Exception — a run-time error that can be anticipated and handled with try/except.
B3 · Object-Oriented Programming
Class — a blueprint defining the attributes and methods an object will have.
Object — a specific instance created from a class.
Encapsulation — bundling data with the methods that operate on it, restricting direct outside access.
Inheritance — a subclass reusing and extending the attributes/methods of a parent class.
Polymorphism — the same method name behaving differently depending on the object calling it.
Composition/aggregation — modelling "has-a" relationships between objects, with or without shared lifetime.
B4 · Abstract Data Types (HL)
Abstract data type (ADT) — a data structure defined by its operations, not its internal implementation.
Linked list — a sequence of nodes, each pointing to the next, allowing flexible insertion/removal.
Binary search tree — a tree where each node's left subtree is smaller and right subtree is larger.
Hashmap — a structure that maps keys to values using a hash function for near-instant lookup.
A1 · Computer Fundamentals
Fetch–decode–execute cycle — the repeating process a CPU uses to run each instruction in memory.
Register — a small, very fast storage location inside the CPU.
Pipelining — overlapping stages of multiple instructions to increase throughput.
Logic gate — a circuit implementing a basic Boolean operation (AND, OR, NOT, etc).
Scheduling — the OS deciding which process gets the CPU, and for how long.
Interrupt — a signal that pauses the CPU to immediately handle an urgent event.
A2 · Networks
Topology — the physical/logical layout of how devices connect on a network.
Protocol — an agreed set of rules that lets devices communicate correctly.
Packet switching — splitting data into packets sent independently and reassembled at the destination.
Firewall — a system that filters network traffic against a set of security rules.
Encryption — scrambling data so only someone with the correct key can read it.
A3 · Databases
Primary/foreign key — a primary key uniquely identifies a row; a foreign key links to another table's primary key.
Entity-relationship diagram — a diagram modelling entities and how they relate, before building tables.
Normalization — organizing tables to reduce redundancy and avoid update anomalies.
SQL join — combining rows from two or more tables based on a related column.
Data warehouse — a central store consolidating data from multiple sources for analysis.
A4 · Machine Learning (HL)
Feature — an individual measurable input variable used by a model.
Regression — predicting a continuous numeric value from input data.
Classification — assigning input data to one of a set of predefined categories.
Overfitting — a model learning the training data too closely, hurting performance on new data.
Neural network — layers of connected nodes that transform input into an output through weighted connections.
Case Study · Generative AI for Image Creation
Diffusion model — a model that generates images by learning to reverse a noise-adding process.
GAN — a generator and discriminator trained against each other to produce realistic output.
Hybrid model — an approach combining diffusion and GAN techniques to balance quality and speed.
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