Concepts
The IR fundamentals that underpin everything in search. Don’t try to read all of these at once — for a guided foundation order, see How to Start a Career in Search. If you learn only three: BM25, Precision and Recall, and how to measure a ranking change (NDCG + Judgment Lists).
A
- A-B Testing for Search · ACORN-1 · Adaptive Retrieval · Adversarial Relevance Judgment · Agentic Memory · Agentic Query Workload · Agentic Search · APD · Approximate Nearest Neighbor Search · ASH · Asymmetric Re-ranking · Asymmetric Semantic Search · Autocomplete
B
- Bag-of-Documents Model · Bayesian BM25 · Bayesian Optimization · BBQ · BERT · Bi-Encoder · Binary Quantization · Block-Max WAND · BM25 · Box Embedding · Brier Score · Brute-Force Vector Search
C
- Calibrated Relevance Probability · Clean Context · Click Models · Click Signals · Clicks Residual · ColBERT · Collocations · ColPali · Compositional Embeddings · Compositional Queries · Compute-Storage Disaggregation · Concept Vectors · Consistency Filtering · Context Engineering · Contrastive Gap · Contrastive Learning · Conversational Search · Cross-Encoder
D
- Denormalization for Search · Dense Embeddings · Dense Passage Retriever · Dense Vector Retrieval · DICE · Differentiable Search Index · Dimensionality Reduction · Direct Corpus Interaction · Distribution-Based Score Fusion · Diversity Metrics
E
- Economics of Search · ELSER · Embedding Fine-tuning · Embeddings · ERR · Expected Calibration Error · Exploration vs Exploitation
F
G
H
- Hallucination Detection · Hard Negative Mining · Hashing Trick · HippoRAG · Hit Rate at K · HNSW · Hybrid Search · Hypothetical Document Embeddings
I
- Implicit Judgments · Impression Bias · Intent Drift · Inter-Annotator Agreement · Interleaving · Isolated Feedback Loops · ITQ · IVF
J
K
L
- LambdaLoss · LambdaMART · Late Interaction · Learned Sparse Retrieval · Learning to Rank · Levels of Judge Agreement · Linear Score Combination · Listwise Relevance Evaluation · LLM as Judge · LLM Guardrails · Long-Context RAG · LoRA · LSH · LTR Feature Engineering
M
- MAP · Matryoshka Embeddings · miniCOIL · MMR · Modality Gap · Model Context Protocol · MonoT5 · MRR · Multimodal Embeddings · MUVERA
N
O
P
- Pairwise Relevance Evaluation · PCA · PEFT · Personalization · Poincaré Embedding · Pointwise Relevance Evaluation · Pooling · Position Bias · Precision and Recall · Presentation Bias · Prompt Compression · Prompt Optimization · Prompt Sensitivity · PROMPTAGATOR · Purpose-Built Agentic Search Models
Q
- QLoRA · Query Expansion · Query Relaxation · Query Rewriting · Query Routing · Query Sampling · Query Segmentation · Query Specificity · Query Types · Query Understanding
R
- RaBitQ · RAG · RankGPT · Ranking Objectives · Ranking Signal Selection · RankLLaMA · RankNet · Reciprocal Rank Fusion · Region-Based Representation · Reinforcement Learning for Calibrated Decisions · Reinforcement Learning for Search · Relational Transformer · Relative Score Fusion · Relevance Feedback · Reranking · Results Boosting · Results Merchandising · Retrieval Pipeline · RQ-VAE
S
- Scalar Quantization · Score Normalization · Search Architecture · Search Evaluation · Search Governance · Search Intent · Search Results Explainability · Search Scopes · Search Team · Search-R1 · Semantic Boosting · Semantic IDs · Semantic Relevance · Semantic Search · Session-Based Evaluation · Set-Theoretic Embeddings · Sharding · Signal Downboosting · SIRA · Sparse Embeddings · Sparse Vector Retrieval · Spelling Correction · SPLADE · Staged Judging · Statistical Significance in Search Evaluation · Steering Vectors · Stopwords · Synonyms · Synthetic Query Generation · System One Model
T
U
V
- Vector Filtering · Vector Index Updates · Vector Quantization · Vector Search Evaluation · Vector Similarity Metrics · Vertical Selection
W
- WAND · Word2Box · Word2Vec · Wormhole Vectors
Z
Related
- Topics · Tools · Case Studies · People