Clusters refer to a content architecture model where you organize multiple related articles around one comprehensive pillar page. The pillar covers a broad topic at high level while cluster pages dive deep into specific subtopics, all linking back to the pillar and to each other where relevant. The structure works because Google's algorithms now prioritize topical depth over individual keyword density. When you publish 8-12 cluster articles supporting one pillar, you signal expertise in that subject area. A pillar on "commercial real estate investing" might have clusters on cap rates, 1031 exchanges, tenant improvements, property management software, and financing options. Each cluster targets long-tail queries while the pillar ranks for the broader head term. At Ottawa SEO, we typically build clusters when a client wants to own a category, not just rank for isolated keywords. The math matters: one pillar with ten 1,200-word clusters outperforms ten disconnected 1,500-word posts because the interlinking creates semantic relationships Google can map. Key elements of effective clusters: - Pillar pages run 2,500-4,000 words and cover the topic comprehensively without going too deep on any one aspect - Cluster pages target specific search intent with 800-1,500 words each - Internal links use descriptive anchor text, not generic "click here" phrases - URL structure can reflect the relationship but doesn't have to—what matters is the linking pattern The mistake most sites make is building clusters that don't actually relate or answer different user intents. If three of your clusters could be combined into one article, you're diluting authority instead of building it. We've also seen agencies create pillar pages that are just glorified category pages with thin summaries—those don't rank because they add no unique value. Clusters work best for industries where buyers research extensively before converting. For pure transactional queries or very narrow niches, a simpler site structure often performs better without the overhead of maintaining interconnected content groups.