Apache Spark is a widely used open-source framework for real-time processing and analytics of large streams of data. It provides powerful tools for data processing, machine learning, and more, making it a popular choice in the field of big data and data science.

A neural network without any hidden layers is often referred to as a "Perceptron." It consists of only the input and output layers, and it's the simplest form of a neural network.

To handle low-frequency categories in the "Brand" column, you can group the brands based on their frequency. This reduces the number of sparse categories and can improve model performance. You can also consider techniques like label encoding or one-hot encoding, but they might not be ideal for low-frequency categories. PCA is used for dimensionality reduction and not for handling categorical variables.

The method in transfer learning that involves freezing the earlier layers of a pre-trained model and only training the latter layers for the new task is known as fine-tuning. Fine-tuning allows the model to retain the knowledge from the source task while adapting its later layers for the specific requirements of the target task. This approach is common in transfer learning scenarios.

For exploring sales patterns and seasonal trends, time series plots and heatmaps are excellent choices. Time series plots can reveal trends over time, and heatmaps can show correlations between different regions and sales data, helping identify anomalies and patterns.

A bar plot is used to visualize the distribution of a single variable across different categories or groups. It displays the data in rectangular bars, making it easy to compare and understand how the variable is distributed among the categories. Commonly used in Exploratory Data Analysis (EDA).

The hidden state in an RNN is responsible for passing information from one step in the sequence to the next. It carries information from previous steps and combines it with the current input to capture sequential dependencies, making it a crucial component in recurrent neural networks.

XML and JSON are examples of semi-structured data. Semi-structured data is characterized by a hierarchical structure and flexible schemas, making it a middle ground between structured and unstructured data. It is commonly used in various data exchange and storage scenarios.

The "Model Deployment" step in the Data Science Life Cycle is essential for taking the data science model from development to production. It involves integrating the model into real-world applications, making it a crucial phase.

Text data from social media platforms is typically unstructured. It doesn't have a fixed format or schema. It may include text, images, videos, and other content without a well-defined structure, making it unstructured data.

HDFS (Hadoop Distributed File System) is the primary component in the Hadoop ecosystem for distributed data storage. It is designed to store large files across multiple machines and provides data durability and fault tolerance.

The Pooling Layer in a CNN is responsible for reducing the spatial dimensions of the input. This layer downsamples the feature maps, which helps in retaining important features and reducing computational complexity.