'Click-Through Rate' (CTR) is a crucial metric in digital marketing that measures the percentage of people who click on an ad after seeing it. It is calculated by dividing the number of clicks by the number of impressions. In this context, the blank should be filled with "Rate."

Apache Flink is a powerful tool for real-time stream processing in the Big Data ecosystem. It allows the construction of complex transformation pipelines for analyzing and processing data streams in real-time. Apache Kafka, Apache Hadoop, and Apache Spark serve different purposes in the Big Data landscape and are not specifically designed for real-time stream processing.

The median is the middle value in a sorted list. It is not affected by extreme values and provides a measure of central tendency.

The CONCATENATE function is used to combine text from two or more cells into a single cell in Excel. It allows you to concatenate, or join, the contents of different cells.

Classification is optimal for predicting patient readmission risks in healthcare. It involves categorizing patients into different classes, such as high or low risk, based on relevant features. Regression, Association Rule Mining, and Clustering are not as suitable for this specific predictive task.

Prim's Algorithm is used to find the minimum spanning tree for a connected weighted graph. It starts with an arbitrary node and greedily adds the shortest edge that connects a vertex in the tree to a vertex outside the tree until all vertices are included.

Data integrity in a DBMS is ensured by enforcing constraints like primary keys and foreign keys. These constraints maintain the accuracy and consistency of data by preventing invalid or inconsistent entries.

Cloud-based analytics platforms often leverage streaming technology to process and analyze data in real-time, allowing for timely insights and decision-making. Streaming technology enables the continuous flow of data for immediate processing.

The process of transforming raw data into meaningful insights using BI tools is known as Business Intelligence (BI). This involves various activities, including data extraction, transformation, loading, analysis, and visualization, to derive valuable insights for decision-making. Data Analysis and Data Mining are components of BI, while Data Transformation is a specific step within the BI process.

Webhooks allow real-time data updates by triggering events when there are changes on the social media platform. Rate Limiting is more related to controlling the number of requests, OAuth Authentication is for secure authorization, and Swagger Documentation is a tool for API documentation.