ncatlab.org
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nLab is a collaborative online wiki for higher category theory and related areas of mathematics and theoretical physics. It provides definitions, expository articles, and bibliographies on topics such as homology, homotopy, infinity-categories, and higher algebra.
More resources on Homology
Topology Without Tears
Free PDF with homology intro
Hatcher's Algebraic Topology
Free online book with detailed homology chapters
Elementary Algebraic Topology
Learn the fundamentals of homology with Robert Ghrist's Elementary Algebraic Topology course! Explore topological spaces & their algebraic structure.
Algebraic Topology
Learn homology with N J Wildberger's Algebraic Topology course. Explore fundamental concepts with this engaging video playlist!
mathworld.wolfram.com
MathWorld is Wolfram’s comprehensive online mathematics encyclopedia offering detailed, accessible articles on topics across math, including algebraic topology; each entry features definitions, key concepts, theorems, examples, diagrams, formulas, and extensive cross-links to related topics.
ocw.mit.edu
MIT OpenCourseWare provides free, openly licensed MIT course materials across a wide range of subjects, including mathematics and topology. You can browse courses to access lecture notes, assignments, exams, and video lectures to study topics like homology at your own pace.